Looking at the video it looks like 18650 batteries in a casing that allow them to be replaced without any soldering by just putting them in slots like you do on consumer devices with AA or AAA batteries.
Plus when current is flowing, where more resistance is encountered will be the places where more heat needs to be dissipated, and solder melts too easily. Which is why they factory-welded them at instantaneous temperatures beyond the melting point of the interconnection itself.
Right means that the cells must be installed in the correct orientation, must all be the same make, model, and age, and must meet the continuous discharge rate requirement for the application.
I'm sure someone will find a way to get it wrong, but people also find ways to mishandle fuel for internal combustion vehicles with predictable consequences. The accident rate doesn't need to be zero for this to be a good idea.