Can't figure this one out!

Car has been sitting for about a week since I haven't had a chance to get to the alternator belt yet.

Went into it yesterday to pull out my headunit to sell, disconnected the regular adaptor/amp plugs/radio antenna, took about 30 seconds, didn't have to cut any wires. Went and sold the headunit, and when I came back the brake lights were on...wtf?

Got into the car, tried messing with the brake pedal thinking maybe it was stuck, but no luck! Never had this problem before.

Did I hit a wire somewhere just right or something? Any help would be great...