Well, I don't like revolvers. The (single action only) trigger pull is harder and as such, the accuracy gets sacrificed due to the extra finger movement during pull. If he had a high-capacity, say a 16 rnd 9mm XD or Glock or Beretta or whatever, he would have better chances of hitting the bad guy.
Nevertheless, the situation you describe is a bit weird and I don't know all the details. If he had a fair distance from the perp and was pointing his firearm towards him, he should have been able to react on time and stop the threat.
But of course, apart from the technical side of things (learning how to handle a firearm) there is also a mental aspect, ie. being focused and not cracking under pressure. This is the difference between well trained and badly trained cop/security guard/soldier.
This can also happen due to the low crime rate in some places where the police officiers are just not used to pulling out their guns and actually using them (other then on a shooting range).