If the car has cup holders, it would be reasonable for the manufacturer to know that someone may have a drink in that car and that the drink may be spilled on the driver's seat.
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that was what I was alluding to in my post.
Even with that, there are many problems to overcome. There is no power to the motor unless the operating switches are activated. You can put a motor under water and nothing will happen to it if there is no power running to it.
Many vehicles don't even have the switches on either the side or the front of the seat base but on the door so there would be no power what so ever near the motor unless you were actually operating the seat.
Then, even if it got wet, it is very unlikely this would happen. For it to cause a fire, it would have to cause a short that was low enough resistance to allow enough current to flow to cause enough heat to ignite some combustible material close by. The short would also have to be of high enough resistance so there isn't so much current flow the fuse for the circuit blew. It would have to maintain that shorted condition long enough to produce enough heat to ignite some material and if the fluid is causing the short, it simply isn't going to happen because the fluid would evaporate from the heat.
Then, you need to realize where the drive motor actually is. It doesn't set on the floor and is completely covered by the seat above it. There is very little exposed from the side, if any.
So, if you are setting in a car, spilling liquid on the motor and having it cause a fire are extremely remote, if at all possible. If the door is closed, it would be very difficult to actually wet the motor. Fluids spilled on the door side would likely end up on the carpet between the seat and the door jamb. If spilled on the seat, the fluid would either run to the rear of the seat bottom, or be soaked up by the fabric of the seat and further blocked by the foam cushion below the finish material.
It is more likely the cigarette he dropped when he was hopping up off the seat he dumped his beverage on to avoid getting a wet crotch caused the fire.