Interesting. I also grew up in the Deep South, but people are always surprised to hear it, claim I "don't have an accent", etc. And yet, the quiz positively identified me as having a Southern accent.

I assume it's because this quiz is only asking about how we pronounce words, and doesn't measure any other speech metrics like tempo/cadence. I guess I don't have the drawl, but still pronounce words with a Southern accent. Maybe this is why it confuses me so much when my wife pronounces Don and Dawn the same, which was question #2 on the quiz. ("Wait, which person are you talking about?!")

Maybe you have the drawl but not the Southern pronunciation?