Don't think there are anything to burn on a NLAW Projectile, it is not a rocket, it don't have fuel, it have an explosive warhead, it certainly would not catch fire when it bounce off.
Also, it does not explain why the burning is on the bottom of the turret. As I said, as weird as it was sounded, even if it did catch fire for some reason, the fire is does not exist on the outside, which only lead to one logical conclusion. That is the fire is happening on the inside.
Also if you have enough shape charge HE on that warhead, it can punch thru the top Armor of any tank, as it is around 10-20 mm RHA, and NLAW is designed to to an Armor piecing weapon, well, at least it was advertised as so.
So yes, in my opinion, the warhead punched thru the turret and exploded on the inside, and it start a fire in the crew compartment. I have seen enough AT missile hit a tank to come with this conclusion.