Umm, I wasn't joking or anything... You honestly just exploded some unburnt fuel. It's no big deal at all... This is very common, my car does this every time I run it up to like 7000 and let off fast. If you have an Atmospheric venting BOV it will amplify it even more, as the car runs rich for taht split second. If your car drives fine, runs fine and has all it's fulids retained this is what happened. Try to replicate it like this:
Put it in second and cruise around 3.5k rpms for like 20 sec. Then hit it WOT and take it all the way to 7200, then shift quickly to third. Should go BOOOM! Do this at night, and watch your rearview as you shift. You should see a small fire-ball exiting your exhaust. Oh the joys of turbos!