Has there been a case in court were a cyclist has been prosecuted for pushing a bike on a footpath? a good tactic is to carry a copy of any court case and just hand it to the person doing the moaning. if it is a grey area then he cant really enforce it and having something for him to read might sway him.
I had this very same issue with a farmer last year, i had no idea it was a footpath i was on as it was a farm track but i just truned around and left to save the agro.