I know what's happening in this but can someone explain to me why it's happening?
As a fencer, this situation is probably happening because the guy on the left, Choi from Korea, just got a touch against him. He, however, believes that the touch was off-target on the upper hamstring. The white light going on in the background shows that when he is hit in the upper hamstring it is, in fact, off-target and there is nothing wrong with the electronics/his lamee/his opponent's foil.
What probably happened in the bout was the fencer on the right's tip flicked downward and hit the clip connecting Choi's lamee to his body cord and then slipped downwards hitting his hamstring. The first hit on the clip would register as on-target but Choi wouldn't have felt it. The falling tip hitting his hamstring he would have felt, but wouldn't have registered an off-target as the on-target was already showing.
Ultimately: touch, right.