I thought it was odd too. Thing is there were only 5 or so people in the gym, and none of them I knew.Sounds odd. Maybe it was a friend playing a joke on you?
Trust me it wont happen again! Dumb mistake....Dude...never leave your keys in your gym bag. Don't even leave them on the key hanger that a lot of gyms have. Either lock them up in a locker or keep them on your body...just saying. I never leave my keys anywhere...especially at the gym.
^^^^^^Thistime for a home gym.