Dead ends "in the green area" don't matter. The green walls are contiguous (connected), and the blue walls are also contiguous, but green and blue don't touch

Dead ends "in the green area" don't matter. The green walls are contiguous (connected), and the blue walls are also contiguous, but green and blue don't touch anywhere. So the border between the green and blue sections defines the path. If you made the maze into a physical model, with walls but no floor or ceiling, the green and blue sections would "pull apart" from each other along that border.