Bottle Bomb?

OK, I've read about bottle bombs on brew boards and heard people talk about them but it's always been while the bottles were sitting and bottle carbonating (too much sugar seems to be the main cause.) Hadn't had this problem myself, but I took out a bottle of the blonde ale that is currently bottle conditioning. The last bottle I filled was only half full, I figured that would be a good one to check the carbonating progress. Didn't refrigerate, just took out a frosted mug to put it in. Applied the bottle opener and the thing started to gush! Pushed the cap down with my thumb and ran for the sink. Lifted my thumb and the thing went off like a shook up champagne bottle, almost lost an eye! Anyway, cleaned up my mess and tried the beer, not bad, tasted kind of flat for all the carbonation.

Not sure if it was the half bottle, not refrigerating or something else, I'll wait till the weekend and try another, open it OUTSIDE this time....