If we ignore the foul play, why didn't the ref give a penalty for not rolling away. The tackler is clearly in the way of arriving players and makes no attempt to roll.
If this has been a trend in the game it often rises players frustrations and you get a result like this.
A fair point that you raise UpandUnder.
It may well be that the referee was already verbalising that there was a PK advantage coming for the player not clearing the tackle zone in a timely manner, the referee was pausing (the phrase is "Let it Breathe") to see what material effect the actions of the defending player are having on the options for the attacking team.
Not withstanding the fact that Flood will have known that under any circumstances that you do not take the Law into your own hands and you certainly don't make contact with the body of a prone player with the boot.
Granted that at the lower levels you would look to signal and verbalise advantage quicker so that you prevent player frustrations getting out of hand.