I don't think "foreshadowing" is relevant with Astarion after seeing bloody fangs in loadscreen art or reading "centuries old vampire" in his origin character description.
Same goes with Wyll being coy about having a patron or (according to some) Shadowheart acting like her armor isn’t a dead giveaway.
There are plenty of secrets to be missed in BG3, but the companion’s secrets are simply their backstory. It’s necessary for the player to know these things for the narrative to make sense. I think that’s why Larian are using the blunt end of the foreshadowing stick.
