I don't think that's actually slow motion on the rotor, it's just that their speed matched up closely with the FPS that the camera was recording in, giving the illusion of slow motion.
Very cool what Sikorsky is doing though, I work with people that designed the T800 engine that powers that thing and it's great to see it getting used for something cool like that, it's a great engine that unfortunately had the program it was designed for get cancelled.
I also like Sikorsky's attitude about the development of this aircraft. From what I understand they pitched this idea to the military and when the idea was shot down they basically said "Screw you guys, we're going to do it ourselves".
They have a nice set of blades being used just for forward thrust, so cheating.
So moving to a better design that fits what you want your aircraft to do is cheating? It's still a helicopter, it still can hover, it just uses a counter rotating blade to prevent rotation and a pusher prop to get it moving even faster. It's a great idea that allows them to take the benefits of rotorcraft to a much faster vehicle without resorting to a tilt rotor like the V-22 ospery.