Was it the finger flick that did it? Well, that was the tool. Lam used a physically strong tool to attack a physically weak target.
He "won" that encounter not by being stronger (he wasn't), or by knowing more "techniques" (though he did). He won because he remained calm in the face of danger. By remaining calm, he saw his opportunity and was able to take it. Of course, if he had panicked, it would have been different.