You cannot physically detect a concussion.
Interestingly, however, the amount of trauma during and immediately after a collision is a good predictor of intense symptoms.
In any event, I would absolutely not rule out the knock he took affecting his performance, even if it weren't a full blown concussion.
Personally - as someone who has suffered one - I find it odd that he wouldn't have noticed something strange and asked for assistance / to come off straight away... especially after the first blunder... but then again who knows.
