Well tbh fam, the alliance did provoke the fight in stormheim for once. It's even clearer when you play alliance. It's admiral Rogers going ham on the horde. It's made explicitly clear.
Genn says that she's free to take them out if they threaten the mission to find the pillar, and she just says that right, they WILL be found a threat, no matter what. Next second the intro plays with the skybreaker bombing the forsaken ships.
Not saying they don't quite deserve it for what slyvi is up to, but there was no way to know that at this point. So yeah, unprovoked.