Who knows. The college saga has a lot of unanswered questions, first of which is "did he actually attend in any meaningful sense?" We know that he (read: Heather) bought a schoolgirl outfit and some paleolithic textbooks, and he asked some questions on Twitter about pre-calc stuff, but beyond that all we "know" about his scholastic career was his constant claims of scoring a billion percent on everything. Inasmuch as we know that he's a gross exhibitionist, we know he would have been posting those tests if they'd existed, just like he'd have been shooting selfies at the TRUE and HONEST pride club that was wall-to-wall with transfemmes in stripey socks and cat ears. Hell, if he'd been getting federal assistance, we'd know because Satana wouldn't be able to resist showing off his brand new Bad Dragon masterpiece collection. But none of that happened.
Broad theory that fits all the available data: he audited some classes as an excuse to look for some strange on campus, did the occasional bit of coursework when he felt like it, and pretended he was going to school so Heather would play along (and buy him the schoolgirl outfit.) He failed at cheating (as it turns out, a flabby, aging transvestite with perpetual duckface isn't much of a catch) and pretended the money ran out when Heather started getting on his case about graduating and going to work. There never was any money.
Obviously, Zach watchers more astute than myself may have better theories.