You are very, very fortunate that nothing bad happened. And, so am I. I still shudder when I recall a time when a stem cracked on me while I was riding my bike at the start of this 1/2 mile 14% grade. I noticed the problem just in time. We all just need to inspect our equipment regularly. And hope for the best. In my case, I believe it was just a defective stem and not the result of over-torquing; but, as Timothy says, over-torquing is often the problem.