The hydrostatic shock of a bullet hitting near the spine can indeed produce enough pressure to momentarily shut down the nervous system from that point rearward. Sometimes it's permanent, and sometimes it's not.

You see the temporary effect with neck shots too. They are knocked flat, and then get up in a few minutes and run away like you missed. I hear many hunters are so surprised to see the deer get back up that they don't shoot again to bring down the already wounded deer.

Gotta be ready to take that second shot. If one goes down like that again, I'd close in quick and be ready to fire.