Obviously its not a demo build, its the start of the game. They are literaly shwoing the first 10 minutes of the game, why put in cameos when you gotta take em out later again? Especialy when youre so early in development
I don't know if that's what game developers normally show off at PAX but that booth was a prime opportunity to put many fans at ease as far as lore continuity, the setting etc. When it comes to cameos, a tutorial area would have fit such a purpose perfectly. I think many people will happily give BG3 a chance regardless of their preferred combat system if it acknowledges past games in some way, form or shape.