There's nothing atypical about that in the graphic design world.

An artist does not own "their" style, and can even be one of thousands of people drawing in that same style.

Art styles are not something people can own.

Imagine trying to own a genre of music...

You’re ignoring what I said. It’s one thing to draw in a similar style, it’s another to market it as a style using someone else’s name and portfolio to get clout.