Those wheels would not have been turning but skidding along the concrete.
Which suggests that brakes alone are useless under engine test conditions and presumably chocks should be used to stop forward motion of the aircraft? I thought the consensus earlier in the thread was contrary to that?
In any case, I find it difficult to believe that something so large with so much inertia AND brakes on can attain 30 knots in such a short space of time unless the wheels were turning.