So Aradin talking shit to Zevlor about how tieflings aren't known for their bravery might be an actual personal attack against Zevlor, since there's a bit of dialogue between him and his right hand in his little enclave room where there's a mention of Hellriders. I don't know if it's ever brought up in BG3 itself since even after 180 hours I've still not finished act 2, but in the setup preamble of the Descent into Avernus adventure path it mentions that the Hellriders were a unit of Paladin knights of Elturel trained by Zariel when she was still an angel for the purpose of invading Avernus to intercede in the Blood War and try to curb some of the destruction it wreaks through the multiverse. Things went south for the unit and surviving Hellriders abandoned the fight and retreated, sealing the portal they used to reach Avernus behind them and abandoning Zariel in the Nine Hells, where she was defeated, captured and corrupted. This set the seed for what would eventually happen to drag Elturel into Avernus by Zariel and the forces she ends up commanding, and in the event that pulled Elturel into the Nine Hells, members of the Hellriders, who still existed as an organization to protect the city as a military force, fled along with refugee civilians. There's bad blood between Baldur's Gate and Elturel historically, so identified Hellriders seen fleeing their duty (as a Paladin order, mind you) were arrested for desertion basically, so they wouldn't cause trouble in Baldur's Gate. Naturally, this is exactly what Hellriders ended up doing, because a number of them seem to believe Baldur's Gate itself is responsible for what's happened. It isn't surprising either, given what this book says about the interactions between Elturel and Baldur's Gate. Elturel seems like it only has ocean access via a river that runs through Baldur's Gate itself, and folks in Baldur's Gate have been just straight up robbing Elturel's trade ships they send up the river to try to conduct trade, so all this tension between the cities is because of the people of Baldur's Gate being fucking antagonistic to begin with.
So, this whole adventure path was also only all resolved some months before the events of Baldur's Gate 3 begin. When Aradin is talking shit to Zevlor, it's not random racism for the sake of being an asshole. He's talking shit to someone that might have abandoned his holy duty to defend his home and may have additionally fought against the authority figures of another city to avoid being detained as actual wildcard threats to stability among a throng of panicked refugees fleeing the planar deletion of their city. Baldur's Gate had to basically enter lockdown to keep Elturelan refugees out of the city to try to keep things somewhat in order, the Flaming Fist were busy dealing with all that business and the rogue Hellriders, which meant there wasn't enough law enforcers focusing on the rest of the city to deal with the sharp spike of murders that began for the sake of the Dead Three. Murders orchestrated by one of several big bads of the adventure, who incidentally, was also an Elturelan refugee. TURNS OUT THERE'S A LOT OF BAD BLOOD, with very understandable reasons just in the lead-in to the set up and I've not even gone 14 pages into the book. It's actually not even just broad mistrust for a race with some very real infernal complications, but actually just remaining resentment over hilariously recent political tensions between actual rival cities that at it's ultimate result could have seen Baldur's Gate pulled into Avernus as well thanks to the actions that had taken place in secret up to this point.
Now, a bit of research suggests Zevlor might not have been one that fled Elturel when it was taken, so he could have stayed to defend and survived the whole ordeal. He's not in the adventure proper, so he's non-canon to the broader story there at least, but unsurprisingly seeing as this whole-ass city gets pulled into the Nine Hells and returned there would obviously be some tension with the devilkin Tieflings. To no surprise, the Zariel, Asmodeus and Mephistopheles bloodlines in the game are representative of Zariel, a major antagonist of the adventure, Asmodeus as the one that corrupted her (and a god in his own right) and Mephistopheles is also mentioned somewhere in the book I've yet to see. What a shock that the three bloodlines associated with a very recent devil contract shenanigan attack on an entire city would cause some consternation among the citizens. Sure, it's misplaced bigotry against people that really didn't have anything to do with it, but lumping back in to the past discussion on the nature of fiend blood and the fact that all this shit just fucking happened in the first place, again it really can't be faulted. Look at reality with how any brown-looking motherfucker got treated when a couple of planes slammed some tall buildings in New York, but consider the further implications of what if instead of political ideology, it was remote puppeteering through devil taint that drove someone to commit a terrorist attack? I'd be inclined to agree with the notion of casting out some redskinned motherfucker whose blood runs with the power of the gigachad demon daddy that just dragged an entire city into hell to be assrammed by pit fiends.
Also unrelated to all this above but still within context, Ulder Ravengard, the big Duke-man of Baldur's Gate that went and got abducted by the Absolute cultists? Yeah, he was bamboozled by two of the antagonists of this adventure path and got trapped in all this shit too. This motherfucker just cannot stop being captured by devil worshippers, meanwhile his own damn son Wyll goes and makes a fiend pact with a cambion. Stay losing, Ravencuck.