I still think the description talking about oils in its skin is hinting at a part-poison typing, Sulphur is pretty poisonous too!
It's definitely a possibility. But I'm always apprehensive about Pokedex entries/descriptions.
After all, Umbreon's description in Gold would have most people guessing it was a Poison type if they didn't know better:
When agitated, this Pokémon protects itself by spraying poisonous sweat from its pores.