It sounds like a shot that impacted very close to the spine and stunned the animal temporarily.That is why I hate neck and spine shots.I was in a similar situation in the past when a friend shot an elk that behaved the same way.We follwed the tracks for a bit,then abandoned the chase.Wecame back several hours later and found the elk nearly two kilometers from where it was shot.It was a long recovery,but we make every effort possible to recover any animal that has been hit.We would have come back the next morning if necessary.