The homeless looking man was probably a paid messenger. given that said guy gave op fifty dollars, his pay would have to be significantly larger to ensure proper delivery. so, lets assume the original source of the note paid at least 150.00 with said delivery fee, sans labor costs for the creation of the puzzle... OK
now, the implication here is that someone thinks they will get a return on their investment. for this to be plausible, op would have to have been deliberately targeted these to receive the puzzle. handing these little surprises out to strangers would not result in a good rate of return.
now, if you are still following my train of thought, it would make sense to assume that these people must have been watching op to think he would be a good candidate to solve the puzzle. yet, if they were they seem to have misprofiled him as he was not able to solve the puzzle alone and so he resorted to posting on reddit.
now, there are a lot of smart people on Reddit, but what are the odds that such a random puzzle would be solved so quickly and for nothing more than karma?
as much as I would like to believe the story, it seems that the simpler explanation would be that it is a fabrication and a viral marketing campaign. this would explain how a fairly complicated puzzle was answered quickly and easily by some redditor, as smart as some of them are I think the odds of someone with both the required skills and willingness to work only for karma finding the post are fairly improbable.
in conclusion we can apply occam's razor to the above argument, to illustrate that it was probably not a bonafide event when compared to these alternate explanations: the man was legitimately crazy (what are the odds if encountering a crazy person with such skills?) or the most likely explanation, that this is a marketing campaign perhaps for a new book, movie, game show, or something else entirely
the argument that op fabricated the story to me is the most convincing, precise and logically sound theory