Here are a few points:
1. Congratulations, you just invented the chain quick release! You can remove or swap chains without needing a chain cutter.
2. You have something in common with Lance Armstrong: youy both finished a ride with a broken chainstay. In his case he broke it in a crash, then really cranked on it, and won a Tour mountain stage. I wonder if a bike could be designed with only one chainstay.
3. It must have been an aluminum fatigue fracture. This has never happened on any of my steel bikes.