Well I had assumed snipers - much like special forces - are given some degree of leeway when it comes to RoE, simply because of how they operate. They are a very long way off, and the fact they have to be so precise often means you need to shoot first, before the enemy knows you're there.
What really confuses me is there was that guy a couple of years back who killed some jihadis from over a mile away, and by all accounts they were just sitting about doing nothing, yet no one questioned his actions then. There was also that SAS sniper more recently who killed three guys through a wall with a .50 cal from over a kilometre out, and again no one had any problems with that. By all accounts, the terrorists didn't see that one coming either.
So I really don't get why this particular incident is playing out the way it is. The man did his job and prevented a rocket attack.