The more that people are exposed to generative AI, the more they're going to sound like it. Just like how kids pick up the mannerisms of their parents and of their friends.
One sentence sounding like AI might even be something you'd pick up from a friend who used AI and started talking like that, so it could even happen to a person who never used AI themselves.
I'm sure this sort of thing is already happening, and I'm sure it will only get worse.