> They're going to be focused on containing the energy not draining it.
In an emergency that involves extracting passengers from an electric car, the most likely outcome is that the battery will get shorted to the car's chassis, at which point the emergency links in the battery will open up, isolating the battery from the rest of the car and its passengers.
As the video explains, even when the battery has been isolated there are other components that remain electrically hazardous such as capacitors and the converter.
Also there is the possibility that the battery itself may be physically compromised in an accident, e.g. it could protrude into the cabin (it sits right under it). Not much you can do to isolate it then.
Caps hold energy, sure, but if you're cutting through one it will self-short, which will be momentarily unpleasant but should not be close enough to anyone to actually injure them. What would be more worrying would be to cut through a circuit without completing a current flow path for the capacitor as that would leave open the possibility of someone accidentally completing the circuit themselves. But even this is not a large risk if you use conductive tools (which will absorb the brief current surge) or wear anything insulating.
The concern with the inverter-converter is mostly due to the fact that it's hooked up the battery. If the battery is already open-circuited then the inverter-converter should just be a dumb block, modulo any residual energy left over in a rectification circuit or something.
In an emergency that involves extracting passengers from an electric car, the most likely outcome is that the battery will get shorted to the car's chassis, at which point the emergency links in the battery will open up, isolating the battery from the rest of the car and its passengers.