Hm? Noivern? Sure. That is true. But it evolves from Noi-bat, not Noi-dragon. And their type is Flying/Dragon.

Things can be both!

[ also yeah birds and bats can breed, but the flying egg group makes plenty of sense, just like how the bug one does. wait until you hear about what complete nonsense the field egg group gets up to, Akechi. ]