If he'd asked them, then fair enough, but just going up and snapping away is out of order.
Given the fact that you say he just turned up and started taking pictures, it doesn't sound like he's a dogger and very llikely not a member here either. More likely to be either be a bad mannered lurker or a resident who has worked out that this behaviour might rid his local car park/beauty spot of doggers....your post gave the impression this was during the day?
for all you know he could have been a reporter
thats why a lot of couples who go dogging dont like their photos being taken
if they do they normally take them with their own camera