I mean, you're right. All birds are dinosaurs, but not all dinosaurs are birds. There are dramatic differences between ornithischia and saurischia, between sauropods and theropods, and between avians and other theropods.
The whole thing has led to some terrible conflagrations in the popular discourse. Nope, just because birds have feathers doesn't mean all dinosaurs did. Only some theropods did. Feather doesn't equal flight feather, see also Kiwis. Nope, not all dinosaurs were endotherms. Ornithischia in particular strongly resembled modern crocodylian metabolisms, while theropod metabolisms were rather variable, from mesotherms all the way to genuine endotherms. Nope, dinosaurs weren't as clever as modern birds, and for that matter, the cleverest birds only evolved in the past thirty million years in the first place. For some reason people discount ostriches' pea brains while fawning over corvids and then think Trex was like that, too, which is just... no. We know Trex' brain resembled an alligator's in overall structure, and its relative size was around the upper range of crocodylians, while the dromaesauridae and troodontidae reached the lower range of birds. Emphasis on lower range.
And the retards drawing polar sauropods and think they're doing science need to kill themselves. Sauropod range was noticeably more restricted than that of other dinosaurs. They liked it warm and unlike other groups of dinosaurs, they never penetrated the polar circle.
