Ah yes, I see.
Here's what I think.
Two things, drive train loss and torque. I believe that although the F10 M5 is almost 1,000 pounds heavier than the Superleggera it has the torque to make up for it. All of it's torque can be used to give the heavier vehicle a lot of momentum. Additionally, the Gallardo is all wheel drive and suffers from much greater drive train loss than the M5. His Lambo is equiped with the E-Gear transmission and is therefore much slower and less efficient at carrying through the power and torque of the engine to both of his diffs, than the M5to it's single and far more efficient Active ///M Differential. The M5's DCT combined with the active ///M differential allow for far far less drive train loss despite the massive disadvantage in weight. In the end I think it's about efficiency. I'm not sure people understand that it's not just about horsepower and torque, it's about how efficiently a vehicle can use those things that wins races. A perfect example is the Tesla Model S. Zero Drive Train Loss, 100% torque from zero RPM in that thing, weighs 4,600 pounds and still beats an F10 M5 in the straight line.
By the way for those pulls, I was only in S2. I wasn't paying attention while I was driving and forgot to put it in S3. I wonder if there would have been a difference.