That is incompetency at it's best. It's common knowledge that anything over 150hp needs strapping down at the rear, and the front so there is zero chance of the car moving.
If you watch the video closely you will the see the dyno operator driving the car turn the wheels whilst "in motion". That is an amateur mistake. What an idiot.
I bet that company's reputation has been ruined tbh. Who would take their car to that company for work doing after seeing that? I know I wouldn't.
A similar thing happened the last time I were at awesome gti in Manchester at a RR day.
Not only did the rollers read high by 10hp but the dyno operator put the car in reverse by accident while it was in motion. Knocked the car off the rollers even though it was strapped down and damaged the wheel and the arch.
The car was a fully restored old mini that was mint. I was disgusted by this because the operator didn't even apologise.
What a joke. I hate incompetent people tbh