I will admit that my first gut reaction was wonder if he is hoping for an 'invite to a play date' cause he is bored and lonely but is too embarrassed to invite himself into your group and is hoping if you could 'see' him that you'd take the first step .... but than I reread it as your neighbor 'above you' so than had a hard time imagining how would you be able to see each other at all and if his door is open cause there would be a floor between you?

Is it his patio door that is being left open a crack ~ cause if so when I lived in an apartment my patio door to the balcony was always open this time of year ~ I was not trying to eavesdrop on neighbors or anything however it is just part of apartment living that you could 'hear' a conversation if they were out on their balcony too?