The reason many of the Forum members urge one not to bring their dog to public dog parks, is because some people don't have control of their dogs, and are not responsible enough to do anything about their dogs misbehaving. It's a place where anything unexpected could happen.
But in your case, yes, I would be angry too! You're dog has as much right to be there as any other. Now, if they saw your dog act aggressively towards other dogs, I would understand. But, that doesn't seem to be the case.
Varick vom Haus Jeffery
Dark Sable, intact male
DDR/West German Show Lines