By FIFA law, the FA are powerless in this situation. The incident was seen at the time by one of the officials, hence it being flagged - even if the wrong decision was made at the time, the episode was nevertheless (poorly) dealt with by the officials, and in that respect, the FA cannot intervene.
Boss has got away with this, but I hope he is dropped for a couple of games because there are kids who will take inspiration from these players and copy their actions. Its disgusting behaviour and not the way to inspire the young talent of today.