I doubt that. People making fan posts on social media are not a representative group of casual players, these are usually the most dedicated (or obssesed) fans. If you engage only with them it might leave the impression this is how it is for most players. Most players are casual gamers, and don't bother obsessing over a game to this extent. I am an older player and don't even have social media where I could make 'fan posts', btw.
Larian likes to post their statistics, but that is just a count of how often players do something in the game. This tells you nothing about why the bought they game in the first place either. I've bought BG3 because I am an old fan of the original series and I like turn based combat. I have tried the romances, because why not, but it would not be (and never was) the deciding factor in buying a game for me.
I think the main reason for BG3 popularity is the one Larian named themselves, their co-op model. This gets the players to invite others, who might not even have heard about the game before. So even if someone has no social media, does not read gaming news or watch yt, or whatever is popular nowadays, they might have heard about BG3 from other people.
Most of my game purchases are made because of recommendations from others. There is just too much sponsored content on social media to follow any trends there.
