Unlike his loss against Silva, which showed his weak ground game. I think his loss against Irvin doesn't really mean anything besides Irvin having insane KO power. Houston and Irvin just both decided to do the right thing to produce that KO. It was like in football, where sometimes the defense just randomly picks the right play that will leave a defender unblocked for a sack. You might say Houston has a weak chin but I don't think there is anyone else that could take a superman punch from Irvin.