Here's a fun fact: speaking as a non-native English teacher, I often see that there are some "mistakes" which are much more likely to be made by natives, oddly enough, and they're usually related to spelling the schwa (compatible vs. *compatable, for instance) or to homophones (they're, their, there). Since non-natives don't typically learn by sound and exposure "alone", as a native might, "translating" spoken into written language is often less of an issue, as both are part of the same package in the second language learning process.

That's why you often see non-natives who make zero spelling mistakes but have weird syntax. I've seen countless texts by students who get their they're/their/there right but write unreadable texts. I've also seen texts from native speakers who are very articulate when writing, but there texts show that their having issues with they're spelling.

Having said that, this is just a very stupid individual. This dumbass is using an object pronoun in the subject position. This is something you learn in the first six months of an English course. I've taught this several times, and typically not even non-natives make this mistake. Assuming he's not speaking a very specific dialect that I'm unfamiliar with, I'd say that this is absolutely not the kind of mistake (if you can even call it that) that a native speaker would make, unless they were really overstressing their two neurons in order to make a ridiculously shitty argument. Their are no wrinkles in there brain.