Interestingly, it is a rule, and the umpire was correct. Rule 17.12e states "a free kick shall be awarded against a player who makes unreasonable or unnecessary contact with an injured opposition player".
The carry on from people like Garry Lyon afterwards was absurd until he found out there was a rule, and then he had to knock it down a gear. Personally I agree if they are out there, go hard- but not off the ball. That is just being a dickhead. And not in the spirit of the game, as adjudged by the umpire.