A Puzzling Christmas Card

I just got an interesting Christmas card from my cousin, with a very strange front.

Hey Sconibulus, I heard you liked puzzles so I thought you might have fun with this, the shopkeep guy said something about making circles around the numbers to get a hidden message for your campus square?

I hope you're having a good Christmas, and don't eat all the cookies too quickly!

I don't think the bit about the cookies is relevant to the puzzle, it just came with a box of very tasty cookies, (that are sadly gone now) but it's been included for completeness.

• Looks like some sort of Minesweeper variant ... Jan 5 '17 at 17:01
• The thing I've seen elsewhere with this sort of layout is a different class of puzzle, but when I try to solve this one as one I get a contradiction. Might just be a blunder on my part. Jan 5 '17 at 17:12
• ... I get the same contradiction twice in a row, so it looks as if my conjecture about what sort of puzzle might underlie this is wrong. Jan 5 '17 at 17:21
• Oops, my editing from an older version of the puzzle wasn't entirely correct, the top-left green octagon is supposed to read 2, while the 3 in the square right of the bottom-right green octagon is supposed to be blank, with the 3 immediately below. I'm working on correcting the image now. Jan 5 '17 at 17:26
• Well, now I've solved it but I'm clearly missing some further cleverness... Jan 5 '17 at 17:38

If we treat the image as a

and solve it, we get this (apologies for my excessive neatness and elegance :-); the blue annotations are because I was working from an earlier version of the image):

but right now I'm failing to see any hidden message in it...

It's obvious to guess that

the green octagons are particularly significant; perhaps e.g. the presence or absence of portions of their edge might indicate 1 or 0 bits in ASCII or something. (It definitely can't be that specific thing. ASCII is a 7-bit code and each of the eight edge positions occurs in both states.)

Nothing of this sort jumps out at me right now, though.

• Maybe it's a problem with your browser. Obviously you need to clear your cookies. I mean, he mentioned the cookies are gone right there in the puzzle story. Glad to help. :)
– Rubio
Jan 5 '17 at 18:01