well....ala mhigo is in close proximity to the black shroud.

due to the sylphs being ruled out, the ixal are also beastmen near the black shroud. I'm not versed into ixali history, but they might have summoned garuda because they felt threatened by the garleans.

though its likely that a native beast tribe summoned their own patron demi-god...or a bunch of ala mhigans summoned rhalgr.