Whirlwind priority?

Was fighting a cult member's Volcarona in the Fiery Caverns and it Whirlwinded me out a couple times. No big deal, until it outsped my Swampert when I used Scald. Either Whirlwind has +0 priority, Scald has -6 priority, or that Volcarona had Gale Wings. I'm fairly certain none of those should be the case.