Alligators are part of the crocodile order, so while all alligators are crocodiles, only some crocodiles are alligators. There are many types of crocodiles all over the world (and the order goes back 84 million years to the Cretaceous Period), but there are only two types of alligators—the American alligator of the U.S. south, and the Chinese alligator, which lives only along the Yangtze River.
https://grammarist.com/usage/alligator-crocodile/
咁其實統稱crocodile都無錯?