Yeah the AI part of their post is stupid, but they're right; screenshots can be easily faked (through e.g inspect element), so if your social media feed is mostly screenshots from other social media, you're at a relatively high risk of seeing fake posts. On the other hand you can't fake the content of a post or repost or the quoted content of a quote post, so if your feed contains only non-screenshot content you can be relatively certain that the content you're seeing is genuine.

I've never had that problem on Mastodon, but I can see how it could be annoying if you follow a lot of people who mainly post screenshots of people's posts from other social media sites. Though you could solve that problem by unfollowing those people...