For the new M6 currently there is not much more available than a tune and exhaust so that is likely what this car has. The advantage it has over the RS6 is a dual clutch gearbox and rear wheel drive which is more efficient from a roll. It also is a couple hundred pounds lighter depending on whose specs you go buy but definitely the lighter car of the two. This race should be closer but without any dyno numbers for the cars or supplemental information for all we know the guy who put up this video (who has extreme BMW bias) may have chosen a stock RS6.
Regardless, video of the beatdown below.