Blick winkel was explained a few posts above you so you could look it up
it's an entity from ever17 game.
Anyway I'm not so sure whether the man on the moon refer to this '?'.. While it's almost certain that this '?' has the same ability as Sigma (and may have some sort of morphogenic field too considering that he took over Kyle's body), I think that line refers solely to Sigma. My reasoning is that this '?' doesn't have much part in this game since he's only introduced at the end (one might argue that the whole game was done by him, but eh) and that it's Sigma who actually has bigger part in the moon. It also might be a ruse so that Sigma will awaken his time jumping ability.
As for whether this '?' entity is a human or BW-like entity... well, I'm more inclined to believe that it's a BW-like entity since he knows everything that happened on the moon. That doesn't mean that 'body back in the past' is questionable. Back in Ever17 we can see that even BW stays in one of the two protagonist which makes him think that he's human before realizing the truth. I believe similar things also happen in this game, hence that 'body back in the past' since he thinks he's a human (because his point of view is solely based on that person A consciousness).
Just imagine that you're doing your life like usual but one day you realized that the 'you' that you thought was your own body + consciousness is actually someone else and that your real body is actually elsewhere. Before realizing the truth, of course you'd think that the 'you' is actually yourself.
Since this '?' woke up as Kyle and has the knowledge of the entire game in his minds then of course he would safely assume that he's Kyle. Remember when we don't realize anything about '?' and the chapter starts playing with us reading Kyle P.O.V? If we assume that this '?' is similar to player representation, of course this '?' will assume that he's, in fact, Kyle (just like us thinking that we're now playing as Kyle).
tl;dr yeah you might say that '?' represents the player but it's possible to say this '?' entity believes that he/she is a human too.
Oh and I don't really think that this '?' influenced what Sigma did in this game. I believe that this '?' just observed what happened in this game and only actually take part during the epilogue when he's in Kyle's body. Since Akane said that '?' would help Sigma and Phi during mars test site... I believe that his actual assistance would be during the next game rather than this game.