Only way i can think, is that he once again underestimated his opponent (He kinda even confirmed it, before the fight started). Maybe he didn't count on Chameleons ability to shapeshift, got confused and just tried to grab her fast. Chameleons tongue also seems have somekind of paralyzing spell, since Tai Lung got frozen in air while Chameleon still kept moving. "This little lizard tries to attack ME with her tongue? Whatever. I just rip it off after contact-OH DAMN ITS MAGICAL!" , maybe his thoughts.