I fully expect Collum to say that the Hearts boy playing the ball with his head was involuntary and that its incumbent on Welsh to watch what he's doing.
Collum is coming out with loads of phrases like 'Normal footballing contact' and 'defender needs to keep out of the way', but the application of this is haphazard at best.
You could say that Welsh getting a 'glancing brush' (remember that one) to the boys head is normal footballing contact, given the context of the play.