This reminds me of the "fun fact" that people throw around about tomatoes being a fruit.

Really there are two sets of terms - culinary and botanical. Botanically tomatoes are a fruit yes, but they are also a vegetable. And in the culinary context you would never use a tomato like a fruit.

The English language is defined by it's usage, and the same word can mean different things in different contexts. Dinosaur is used commonly to refer to Pterosaurs in the "general" context, so a Pterosaur is a Dinosaur in that context. If you were instead a biologist talking in the context of academia then a Pterosaur would not be a Dinosaur.