flash fire from self-cleaning oven
I don't think it really matters exactly what happened. Unless you've left out something important, it's not working right, and you need to get it repaired. The best case is that it keeps burning your food, and the worst case is that you set your place on fire.

If you want to confirm that it's doing something wrong, you could put a thermometer in it and turn it on (no food) and confirm that it's getting way too hot. (Edit: but please be careful, as Aaronut said. If there's any sign things are going wrong, turn it off, and leave the door closed.)