The difference is that the batteries can ignite without an external heat source.
That doesn't necessarily make them more dangerous. I have a friend who lost a home to a fire that started in the engine compartment of a car in the garage. It was probably a leaky fuel line dripping onto a hot engine component. In your reconing is that an internal or an external heat source? Of order half a dozen car fires happen during a typical commute day on SF bay area freeways, and that's not counting the fires that start because of collisions.
It doesn't seem that likely that Teslas are any more fire prone than any other car. The rates for gasoline cars have about one serious (i.e. reported to police) fire per 18 million miles. If the average car goes 180K miles, that's about 1% that go up in flames at some point. The average Tesla hasn't gone that far, and I don't know what the fleet mileage is, but I'll be surprised if they are that flammable.
When I drop a ball, and show that it follows the path predicted by gravitation, what more must I do to "show" that gravity caused the ball to fall.
When the atmospheric CO2 content increases and the global average temperature goes up about the amount Arrhenius said it would back in 1906 due to basic physical principles, and then I show that is in fact human emissions that caused the CO2 increase, what more must I do to "show" that global warming cause the temperature increase.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (5) All right, who's the wiseguy who stuck this trigraph stuff in here?