What's The Deal With This 'Eerily Silent' Camouflaged BMW X6?

A reader spotted this camo-wrapped BMW X6 between Greer, SC and Asheville, NC yesterday claiming he "couldn't hear the exhaust over the tires" as the car/SUV/bulgy Bimmer surged from 80 to "very fast."

Whatever the Bavarians want to call it, all X-Series BMWs are SUVs as far as I'm concerned so I'm claiming legitimate jurisdiction here on Truck Yeah!

There are clearly exhaust pipes, so it's not fully electric. Also based on the exhaust outputs and lack of obscenely swollen fenders; I don't think it's an M. Any ideas on why this vehicle might have been so quiet as it accelerated away from our photographer?

Hat tip to Fordboy357!