Just thinking out loud with no particular expertise in design here ...
The swept wings may just be a compromise between a good place for attaching wings to fuselage, and positioning of the engines for balance and noise reduction to the cabin.
You'd imagine all that wing area below the rotor would make it quite inefficient in the hover.
I guess it would use asymmetric thrust from the props for yaw control?
Interesting idea, and it looks rather cool too (important design feature there!)