As long as the angle between the thrust vector and the weight vector stays below the line through the CG and the rear contact patch you can top 1G. (More thrust and you go over, of course.) The tire can slip and still produce more than enough force for that, though I know the numbers were produced by a pro-level rider, so I doubt there was much wheelspin.
As you can infer from what I just said, the numbers were produced by a pro rider. All the bike mags use them.