Comment by ben_w

If your car suffers a catastrophic exothermic event with its fuel, that looks like a car fire.

If the same energy explodes as antimatter, to the extent that it is not radiation shielded what you get is a pulse of high-energy ionising radiation*; while to the extent that it is radiation shielded, it looks like order-of as many kg of TNT as the number of kWh stored, give or take.

* with a note that 10 joules of absorbed energy per kg of body mass is "if you're lucky you will fall into a coma and die in about a week, if you're unlucky you'll be conscious", and that 1 litre of ICE fuel ~= 10 kWh = 36 megajoules.