He was just back pedalling with nobody around. His knee gave out and he limped to the sidelines. His knee was no longer reconstructed. The knee-flexed position used in skiing is actually very stable for the knees. Many people prefer to ski with a good knee brace to give them protection and they do well when they ski in control.
Skiing is a knee-wrecker sport because of the uncontrolled forces.
Make some lifestyle decisions about how much risk you are willing to take in your sports. Despite a very loose knee you can still climb back on the bull if you want. On the other hand, there are lots of knee-safe sports or safer ways to do sports. You also need to spend lots of time being active and keeping in top shape. Strength and coordination exercises will not tighten the knee ligaments but under controlled conditions, rehab will allow your body to respond.