I agree with wmeredith on this one. Its really the only way it could work, especialy for its point cost. His CC damage is the same as a regular swordsman, same for the bow, and since they are both fire-based, then anything that is immune to fire-based would be immune to their dam.
I also think that he should be immune to fire-based attacks like all the other House Helios Ind. are. That would solve your problem nicely. IMO this was an editing mistake, and he is immune.