I don't care if it was gay, straight, donkey, whatever, they were just idiotic. Depending on what deck their balcony cabin was on, it was probably a very public place. If the pic in the article was of the actual ship, most of the newer cruise ships tower over it. Now add that to the fact that when a ship comes into port (during waking hours) most people who have balcony cabins will usually go out onto theirs and take in the experience. For those with inside cabins, they usually go up to one of the top decks to watch. If there is another ship already in port, many of it's passengers will come out onto their balconies, or go up on deck and wave to the passengers of the ship coming in. From experience, I can tell you that it is a very slow pass by and the view onto the balconies of the other ship are very clear. If they were really that horned up, they should have gone inside their cabin and closed the drapes.
It's just sex.