I think it is that way because he grafted the rear frame and suspension out of an Outlaw IRS. The canted rear suspension was a design element on the Outlaw, IIRC.
Can Am basically used a split swingarm for the rear. Honda / Polaris went for a-arm setup.That's right. They use a similar setup on their big 4x4 quads. On those, they call it the "Rolled IRS". The thinking is that when you hit something with the back tire, the tire pulls up and away from the object (toward the back). Softens the impact of the strike.
I think they really figured out that Can-Am's trailing arm setup is the best IRS on a big quad, so they had to find something that acted similarly but was different.