They transport cars with no gas in them. When I was going to school I used to work part time for a service center that prepped cars for the dealer after overseas transport. There were a lot of things that had to be done. The cars didn't even have oil in the engine.
They transport EV's with a 40% charge which is the industry standard storage charge for Li-Ion batteries. At storage charge a Li-Ion battery is greatly less likely to spontaneously combust due to a manufacturing defect. It can still happen, but a lot less of a chance. More likely an internal short will drain the battery to zero charge before catching fire.
In any case they don't know the cause for sure. They're stating an EV as a possible cause, but it could be anything at this point. They can't know the cause for sure without an investigation and that won't happen as long as it's burning. If the ship sinks there may be no investigation at all.