she used to be a fairly popular artist with the handle/name BSApricot (
Pixiv Link) for a couple years pre VSJ, so she probably got a starting fanbase on twitter that then grew with the VSJ numbers
also im somewhat sure thats common for alot of creators, i know you mentioned twitch followers but the Luxiem boys sans Vox have that trend with their YT subs, 1 Million twitter followers, but only 800k-ish subs for the most part, Vox is the only one with a parity between subs and followers