If this car was just serviced, the fact that they crashed it while testing its brakes is, well, kind of ironic.
We know about the brake test thanks to the video’s description, which informs us that a young mechanic was behind the wheel. As for why he took off in such a hurry and appeared to have steered left towards that pole, is beyond us.
The old Merc doesn’t seem out of control at all. In fact, before the wheels turned left, the driver made a steering adjustment to the right, and the car seemed to respond well without losing grip (which might have imposed further steering inputs).
So then, what happened? Your guess is as good as ours. It doesn’t look like they applied the brakes either (another possible culprit to loss of grip), so perhaps it was just driver error, and a huge one at that.
The two individuals inside the car made a run for it as soon as the W123 hit that light pole, which isn’t the most responsible thing you can do, especially with the engine still running and the throttle seemingly stuck.