They have common ancestors, but it really should be "the crocodiles had split from the avian lineage", with avians including dinosaurs at that moment in time
A split is a split. Archosaurs split into a crocodile line and a dinosaur/bird line--"the avian lineage" (birds being a kind of dinosaur, and the only ones still living) ... that's what "the avian lineage had split from crocodiles" means -- it is not saying that birds are an offshoot from crocodiles, it's saying that the two lines (both kinds of archosaur) split from each other. Likewise, crocodiles are not an offshoot of dinosaurs.
The funny thing is that it would make more sense (going by our popular impression of what dinosaurs looked like) if dinosaurs were in the same lineage as crocodiles, not birds.