I mean, we also technically should be able to determine that Astarion is a vampire. Not just because he's pale with red eyes (could be a albinos or something), but the fangs and bite mark on the neck are quite obvious 😅 (also, it's in the synopsis somewhere, not a spoiler).
However, I understand why they don't do it. They are telling their story.
It's not ideal, but I'm ready to suspend my disbelief over the lack of common sense on this one, because "video game".
If they find a way to allow a religion check (SH) or insight/arcane(?) check (Astarion), that would be nice of course !
I just can imagine that it wouldn't be that simple. I hope I'm wrong, of course
At least we get to learn about their "secret" fairly early on in Act 1, before reaching the Goblin Camp, by simply traveling toward the middle of the map.
If this was pnp, that would be a bit more annoying, to me.
