Mark wasn't familiar with the gay scene and how it all worked, so when the young man linked arms with him he was a bit surprised, but went along with it, obviously!
It seemed to Mark that so much happened through non-verbal gestures, which was just as well as he didn't speak Greek, neither did the young man speak that much English either.
The only thing Mark realised was about to happen which he couldn't allow was the young man to take a mobile phone 'selfie' of the two of them.
Mark couldn't permit any photographic record of himself.