But that's the opposite of what AI tends to do. It tries to predict words that fit a pattern. It wouldn't come up with a new turn of phrase that sounds good because it isn't creative. It has no idea about what "sounds good." It would use a phrase it's seen many times before, because that's what it trained on. Often that ends up being incorrect, but it's written like a normal human would write because it's literally copying what they wrote. It isn't creating new stuff.

College students learning new terms are predisposed to coming up with phrases that aren't common and only partially make sense.

Idk I feel like I've seen this image before the AI craze hit, but maybe I'm wrong.

Some people like creating unusual turns of phrase...

It's probably a combination of autocorrect and the original author not knowing the word "vassal."