To start off with,
'right' => x += 1
'down' => y += 1
In terms of the minemap, it seems kind of counterintuitive visually, but if you're using python, you can check the location using minemap[x][y] to tell you whether you can move to that cell. I'm guessing that's why they set x and y as they did.
If you want to think of it visually, consider the minemap as a list of vectors from left to right, and just transpose each vector in the minemap, now a movement to the 'right' takes you to the the same horizontal spot in the next vector (minemap[x+1][y]) and a movement 'down' takes you to the next entry in the same vector (minemap[x][y+1])

I'm just learning python, but I was able to submit a solution that summed each line instead of ensuring the set was the same (i.e. in a 9x9 sudoku this gave me a sum of 45), this passed all the tests, but I can come up with a test that it would fail (i.e. a 16 x 16 matrix with all 8's)

This was based on Thelonius' solution (I couldn't figure out how to delete this solution entry)