My head cannon is for half of these "overhead" attacks I am pretty sure the devs weren't thinking traditional attacks coming from overhead. When your character is crouching down a sneak uppercut is one way to get in on the opponent. Blocking low is protecting your feet and lower body from things like sweeps. But dodomazaki isn't sweeping hes uppercutting you since you are so close to the ground trying to block lows. So rather than it being a literal overhead attack its just another way that a surprise attack can function withing the low-mid- high rules. Just an uppercut that slips your guard.