Up to this point you’ve presumable figured out that the right columns are the inverse of the left ones, so a 1111 column on the left means 0000 in the right. Also, 2-wide puzzles are mirrored from side to side. You’ve also learned that a bit of stone sticking out means 1 on that side, and conversely means 0 on the other side.
Now for this last puzzle, imagine it’s 2 2×5 puzzles next to each other. The left side’s sticky-out stones correspond to the leftmost column, as per usual, and the right ones to the rightmost column. You now need to do the right column of the left puzzle, and the left one of the right one.
For the left puzzle, the right side would be the right side’s sticky-out bits. BUT, that belongs to the right puzzle, so you invert them. Conversely for the remaining column, and boom you’re done.
As for why the mirroring rule is disregarded, I assume this is because they’re physically not two separate puzzles, they’re smooshed together. Can’t flip the “other puzzle” when it’s not really the other one.