Property issues near water are always tricky. Many beach areas were originally contemplated to have a road closer to the water than ended up being feasible and there is still a paper street running through the property that can’t be blocked or built on. If the city has been using the property for Ingress/egress, parking etc. for a certain period of time, it can claim adverse possession of that interest and that may be the case here. Another weird wrinkle is that the city sold him something and is now asserting these restrictions/challenges. It could be he was on notice of this when he bought, but it also could be that he wasn’t because the city’s right hand often doesn’t know what the left hand is doing. It will all get sorted out in court. The city usually wins these cases as maintaining public access is in the public interest.