What in the crap?

So I brewed a quad like 9 months ago, let it chill for like 3 months then bottled it up. But, of course, since I'm an amateur and don't know what I'm doing really, I didn't re-yeast it. So now I have a flat quad, or so it would seem. I'm going to attempt to re-carbonate it eventually, but the other night, when popping one for a steak marinade, I heard a nice healthy hiss when opened. What in the crap? I've opened probably a dozen of these bastards and this is the only one that carbonated. Maybe all the priming sugar wound up in this one - who knows.. It didn't foam out the top at all. Regular carbonation but the taste did seem super cloying and sticky sweet. Weird.