No. Pseudo legendary Pokemon are those with 600 base stat total and a three stager. Volcarona doesn't meet any of those criteria. It only has 550 bst and is a two stager evolution
Source: https://m.bulbapedia.bulbagarden.net/wiki/Pseudo-legendary_Pokémon
No, it is not.
https://pokemondb.net/pokebase/211795/what-is-a-pseudo-legendary
https://pokemondb.net/pokebase/208465/what-is-the-criteria-in-order-for-pokemon-to-pseudo-legendary
https://pokemondb.net/pokebase/333516/is-volcarona-a-legendary-pokemon
https://pokemondb.net/pokebase/125979/what-is-a-psuedo-legendary?show=125979#q125979
https://pokemondb.net/pokebase/42064/pseudo-legendaries
