Originally Posted by Marielle
I just wanted to understand, at least at what point in the game (in what act and after what events, at least approximately, this dialog can happen)? We've discussed Cazador multiple times

Ah, my bad. This is very early in act 1. My understanding is that to get it you can't have talked/asked about Cazador at all previously, by name at least. It has a lot of flags attached to it so it's a bit hard for me to decode it into a clearer way to trigger it, but I know I've had it several times in early access.
I found this video with the scene I'm talking about, in full release:


My point was that it comes from earlier in development than Ulma, and he seems to imply he's seen Cazador feed (I assumed they'd be dinning in the same room, right?). Which contradicts Ulma's claims that he never corrects. Then again, for all we know: Cazador could've fed in front of Astarion, and it wouldn't have meant that those victims can't become vampire spawn. But I guess Ulma didn't expect that he was turning them to spawn.