I tried 10 and got 9 right. I wouldn't claim to "actually know the fields of study", though I am a mathematician so there were a few where I was able to say "no, wait, that wouldn't make any sense" with reasonable confidence. I did see some mostly-syntactic giveaways other than too-short titles (in fact, I think the shorter titles were mostly the genuine ones for me), such as titles that begin "From ..." but don't have any corresponding "to"; titles with unrealistically long chains of "structure" -- "representations of X over Y-modules over Z over W over T" or whatever; overuse of "Towards ...".
They have a context-free grammar, which is translated by a Perl script into OCaml code which "is also fast, allowing the snarXiv to generate papers even more swiftly than your favorite python script, or Ed Witten in the 80’s."