Exactly why it doesn't matter, it's not an incendiary weapon meant to target ppl in the incendiary way, thus it's not seen as bad of a thing as an incendiary weapon. To put it in other way: that person didn't feel the horrible (and longer) incendiary effect because of the other effects of the weapon. Does it really matter if the person is outside or inside of an armoured vehicle? The actual incendiary weapons are whole different thing.