Correct me if I'm wrong but wasn't that trailer (intro) made while the game was still in it's infancy 2019/2020. So the idea of trying to make sense of it is a bit, ehhh.
Seeing how it presents a game that doesn't exist. (rewrites and all that)
As for the Durge thing, during the EA there were multiple datamines and in one of them it was discovered or rather implied that Tav was a Bhaalspawn. (Remember when Daisy was a thing?) So with that in mind, the og idea of Tav being a Bhaalspawn and being captured might've been different and it could've made prefect sense with what we see in the trailer/intro.
But we didn't get that game, so there are a lot of inconsistencies/ plot holes/ contradictions etc. (whatever you want to call it)
