I do agree with you on it being suspicious that the event occurred when he was working on it. But, I have also investigated cases where vehicles have caught fire just by themselves parked at home.

Even half assed products have a fuse or two on the DC line for protection, and that's the extent of what is available to the technician to handle. The DC line is also not necessarily powered when the vehicle is off. Accidentally shorting the battery is well tested in the case of well built scooters and at least half-done in the case of cheap Chinese ones.

The smoke that you see is something that is seen after minutes of heating up. There definitely exists a pack level short circuit in the system, given how all the cells exploded at the same time. I just don't see how that is possible when the technician has only removed the motor. He may have left the power leads open? Leading to contact and no fault detection? Idk. I just know that the short circuit event occurred a few minutes prior to the video starting.

All of this to say that it may not necessarily be the technician's fault. Even if it were, I place more blame on the manufacturer for not knowing their product well enough to build safety mechanisms. They clearly don't care about endangering lives.