When there is obviously something wrong, as in this instance, the ref should ask the ‘offending’ player if he wants to ‘fess up and remind him that if it turns out that he did actually punch the ball into the net then he would get a substantial fine and a long term ban. Maybe other sanctions such as his club being docked three points.
That’s what ought to happen. The rewards, one point in this case, far outweigh any negative sanctions. He’s a cheat and should be banned from all football.