Is a crocodile technically a dinosaur?

Some other non-dinosaur reptiles are also archosaurs, including pterosaurs (the now-extinct flying reptiles) and modern crocodiles and their ancestors. These and many other types of ancient reptiles are often wrongly called dinosaurs. Marine reptiles, such as ichthyosaurs, plesiosaurs and mosasaurs are not dinosaurs.

What dinosaur did alligators evolve from?

About 250 million years ago, the archosaurs split into two groups: a bird-like group that evolved into dinosaurs, birds, and pterosaurs, and a crocodile-like group that includes the alligators and crocs alive today and a diversity of now-extinct relatives.