This isn't professional wrestling where the outgoing guy is obligated to put over the guy that's staying. AS took that fight for the chance at a title shot. He was serious as a heart attack.
And the fact is that Anderson Silva ALWAYS clowns. That is what he does, both because he enjoys fighting and to try and throw the other guy off his game. Go back and look at his fights. In pretty much all of them he is clowning and taunting to get the other guy to charge into his range so he could snipe him.
Don't get me wrong Kelvin is an excellent fighter and has been far more impressive than I thought he could be. He is VERY dangerous. But he is going up against a superior striker with very good takedown defense and who is also much larger than him.