We're meant to assume correct sentences were written by humans and AI adds glaring factual errors. I don't think it is possible at this point to tell a single human written sentence from an AI written sentence with no other context and it's dangerous to pretend it is this easy.
Several of the AI images included obvious mistakes a human wouldn't have made, but some of them also just seemed like entirely plausible digital illustrations.
Oversimplifying generative AI identification risks overconfidence that makes you even easier to fool.
Loosely related anecdote: A few months ago I showed an illustration of an extinct (bizarre looking) fish to a group of children (ages 10-13ish). They immediately started yelling that it was AI. I'm glad they are learning that images can be fake, but I actually had to explain that "Yes, I know this is not a photo. This animal is long extinct and this is what we think it looked like so a person drew it. No one is trying to fool you."