On the way home, in subway, I have faced that guy once more.

First, I met him at the Lampushka music festival (near to Saint Petersburg, in the forest).
The second time, I met him in a club, and explained where did I meet him before.
That time, I did not recall the place we met before and just talked about his trip to the last Lampushka, made at a different place of the forest.

I meet him everywhere, in the strangest places. His face is so easy to remember, so I just come and say hello trying to explain why/where I met.
It is better to ask him for his name: I sure, we will meet again. :)