piggy backing on the bender of zombies, i think the wall breaker targets first and path finds second, or at least that is how it looks based upon your screen shot.
when you dropped the little guy he picked out the wall in front of that storage because it was the wall piece that was closest to a "trapped" building from it's current position. it then picked a path to get there.
i'll see if i can test this theory out or if it will turn out to be noise instead of signal.

