I think this is an unfair comparison. The "better" AI-generated posters in the article are all much more minimalist.

Minimalist designs have much less opportunity to insert "personality", be it that of a designer or that of an AI. No wonder they look less AI-generated, and when they do it is because some "AI-baroque" slipped through. Fancy unicode characters no human would think of are the salient one in OPs examples.

It'd be much fairer to compare AI and human for the same desired style, and yes a lot of AI-generated stuff is immediately recognizable because no one bothered to tell the AI about the desired style.