I noted this in another post, but who exactly do you think canonically attacked Free Hold? A LOT of the Dungeons are Faction Centered in BfA. I don’t think for a second that canonically it was anyone other than the Horde that dealt with King’s Rest; the Temple of Sethrallis; or Atal’dazar. With that being the case, that means that many of the Kul Tiras dungeons are spearheaded by the Alliance, and among them probably Free Hold (and with it the attack on the Bilgerats).
The Horde had no reason to attack a pirate refuge on Kul Tiras (especially one that is hindering the Kul Tiran navy). Hell, we’re even awkwardly allied with some pirates in that region. The Alliance (and especially the Kul Tirans) in contrast absolutely had motive to break up that pirate den (and kill Eudora, and the other pirate leaders). Thus, the Alliance isn’t just responsible for attacking the Vol’dun Vulpera; they’re also likely responsible for crushing the Bilgerat Vulpera as well.