You reposted a text-based meme that has obvious jpeg compression, so likely you didn't create it (correct me if I'm wrong), but got it from another person/website.

Facebook uses image based pattern recognition and likely matched your image to the same image already in its database, one that they had already written a fact check article for.

My guess is that this fact check is not bot-generated, OP simply posted a meme that has already been fact checked, and Facebook simply used pattern recognition to match the meme with it's corresponding fact check. Don't see anything unusual about that, in fact it's a clever system from a programming perspective.