If someone like me that never uses AI is accused of it, it must be really difficult to differentiate between human and machine writing.

It's more than that, I think. Just like the "increase the contrast to spot AI" folks who've never heard of jpeg compression, the AI witchunters (and I will call them that when they start accusing innocent people of using genAI) have gotten so bad that it almost doesn't matter how you write anymore. I haven't yet been accused of sounding like AI but as a lover of the en and em dashes, colons, et cetera, I feel it's only a matter of time because people were absolutely convinced that any em dash was automatically a sign of the devil AI writing.