Well, many guys don't want to go to clubs where people can see them, simply because they are hiding their homosexuality.
Ah, so they'll naturally go to a public area like a park. Believable.
Actually it is - Especially in countries where homosexuality still is looked upon with prejudice. The darkness of the park gives privacy and reduces the change of being seen entering the gay club.
Assuming this is common in Europe, are you trying to say that this is looked upon with prejuidice there?
It used to be and there still is a lot of men out there that are so insecure in their own sexuality that they think that gay men can "infect" them or something like that. We have come a long way since homosexuality was looked upon as a decease, but gay bashing is still a problem even in Copenhagen, one of the most gay friendly cities in the world (and the park you should stay away from at night time in CPH is Ørstedsparken
http://www.copenhagen-gay-life.dk/index/gay_guide/cruising/rstedsparken)