I thought it was bullet on bullet too, but I think the video made it clear that was not the case. It used some sort of classified countermeasure, now if you also looked it was only good at detonating the explosives in the RPG's, so it would be useless against bullets, mines and IED's, as the video also said.
Now, having said that, what do I think it is? I think it is some sort of microwave technology, sending out a small burst of energy that would somehow detonate the explosives in the RPG's. I doubt it would use lasers or bullets like the CIWS, those require too much time to intercept an RPG, and if it did use bullets then they would likely show up on the screen. I would personally cast a vote for this being some sort of microwave technology, if we can heat up a frozen burrito with a 900 watt microwave I am sure we can super heat the explosives in an RPG.