Actually, all the tracks occur in One Summer Night if you play them before 11:48pm!
The actual relation to the theme was a couple different ways - the premise of the story setup was that the game is free for only one night; and that the game advertises itself as a fantasy world of endless summer nights - where all your dreams come true, living out your wildest fantasies, etc. Summer nights in this context being used as an implication of a setting where you'd let loose and have a good time.
That's at least how ~I~ justified it lmao