I don't think whoever thought of the troop name was aiming for it to be the proper latin word, more likely they just meant to modify the word Inferno (with its meaning in modern english) to a form that sounds more like a name - and the word inferno could very well mean a great fire.
If we insist of applying the meaning of the latin word, it actually means "below" or "underground" - which could be used as "hell" as well, but does not suggest fire or heat in any way. It would make much more sense for Gorgotha to be called Infernus in that case. As for our new mythic, everything about him (if you ignore the name for a second) suggests he's just about fire, and nothing hellish about him. His art, spell, types, trait names, nothing suggests the meaning of the latin word was ever considered (or even known at all) by whoever designed it.