Then you haven't actually seen it! The ball wasn't going in until it hit Walton's back. Walton didn't need to do brilliantly to keep out the header because it wasn't going in, certainly not top corner! He was extremely unlucky that it came down of the crossbar and hit his back. The fact that some idiots allocate the goal to Gestede doesn't change that fact.
Don't think it touched Walton (joys of catchup TV and slo mo ). Hit the bar, bounced down and spun back over the line.