I don't know where it got that idea because I only see a few people using the term "true fish" and they're using the normal definition of vertebrates. If you want to be extra restrictive then there's multiple options. If you really want to exclude tetrapods you might use rayed fish. And there's also bony fish if you think sharks aren't quite right having only cartilage. Who uses jawed fish in particular?

Gpt makes things up. It really shouldn't be used in technical discussions except for a catalyst to find something to look up.