The man knows his own body and if you've had a rib injury than you know it's a bastard to deal with. A bad rib injury makes even breathing hurt. It obviously wasn't that bad since he was able to continue on with his training.
It just looks odd since most guys take an injury that would stop them from fighting on the show very, very badly. If that injury happened to someone else in the semi's I'm sure you would have seen wide range of emotions like anger, sadness - all that.
He was just so calm and matter of fact with not fighting that it looks weird.