Crowley doesn't have much particular interest in the library; he's done some cursory research but he's mostly leaving it to Aziraphale. Which is the reason he's even in the library in the first place. Aziraphale had found a spot to read a novel while Crowley had messed about on his phone, but it's been several hours and the angel is thoroughly engrossed in the book, leaving Crowley to entertain himself.

Someone surrounded by scrolls and books might be fun to poke at, or they might actually have interesting information.

When he does approach and is immediately asked a question, Crowley grins, "S'been two weeks. Someone was about to send in a rescue."