It appears as though based upon its Pokedex description, but I thought it was really rare overall anyway.
Volcarona was never intended to be a legendary, mythical, or the like.
This is firstly because it can breed. No formal legendary Pokemon can breed. Secondly, no official source has ever referred to Volcarona as a legendary Pokemon.
Volcarona is not a 'pseudo-legendary' Pokemon either, as it does not have the traits to be categorised in this way.