Strange does want to know more. About the sigil, about why there was a fight to begin with, about why he's just learning about the vampires now and not when he first signed on.

But he knows that the more he throws at Joker, the less likely he is to actually learn anything. And besides, Childermass is getting information about the sigil. He'll have to trust the other man and focus solely on the task at hand now.

"At this time. Inevitably I'll have more questions for you later, but for now? I just want to know about the vampires." Technically true.