Not only that, but the fire rapidly spread to many more vehicles. I'm not sure of the ratio of diesel to gasoline vehicles in the UK (When I was in France years ago there were a lot more diesel cars than in the US, because of the relative cheapness of diesel at the time) but you can bet that a lot of those were gasoline powered. And once you get to a certain point in the conflagration, the higher ignition temperature of diesel isn't going to make a damned bit of difference. All those vehicles crowded together in a well ventilated space is going to lead to a massive fire.
I wonder if Vixen has been proceeding under the misapprehension that all the structural damage to the parking garage was caused by the one vehicle alone. The way she's been arguing, I'm not sure she understands that the initial vehicle fire was just the ignition point for the greater fire. She also doesn't seem to understand that while diesel may have a higher ignition temperature, it contains about 18% more energy by volume. She seems to have seized on the fact that diesel doesn't ignite quite as easily as gasoline, and inferred that it is much less energetic when it burns, which is simply not the case.