Sounds like beau in "To Kill a Mockingbird"

I was unable to vote as there was no option that he's just a quiet man who keeps to himself and has to contend with a nosy neighbor with an overactive imagination

Chase the stars.

Do something nice.

Or he could be a nice guy who just kinda keeps to himself

Your neighbor sounds a little like me.
I consider myself (as do others) as being a nice guy. I'm not antisocial because... Well, I'm here on this site. Plus I shoot the shit with people I know in person.
I'm just the type that keeps to himself. And tries to be helpful whenever I can.
(Sounds like your neighbor. To me at least)

Introvert, would bet smart well read and pretends to be grumpy but has a good heart. Just because he is secretive doesn't mean he is crazy he might just be a privat sole.

Could be he's an introvert.

Yea I'm going with introvert on this one. None of those answers apply. He does good deeds, that's a good sign. Cookies are a great idea and ice breaker. Let someone know where you are going just in case lol! You can never be too careful.

Update: So after a solid month, this week cookies & cracker candy were made, delivered in a small paper tote, with a note enclosed. The end.

Had to get this off my chest, update #2.
The conclusion is from the original list #7, and not on the list something else.
Former catholic, not a church goer (yay!) but seems to have some sort of baggage that alludes to that time period.
Without going into gorey details, it's been enlightening, my ego got stroked, but for things I won't go into that are out of my margins quirky, one of those things being extremely repressed, my search continues.
He is adorable though, and very sweet. Kind of a shame.
Curiosity sated...