Apparently this diagnostic test came back with a negative "result", but:

-There's nothing but the grade, no submission or anything
-"anonymously graded: no"
-The mail stating it'd been graded claims that happened an hour *after* it was sent

So as far as I'm concerned there's all reason to believe they fucked up somewhere because it's quite ridiculous to me that I'd not write well enough.

I'm sure it'll get sorted out eventually, but guess who's going to be bothered by it all evening?