That sounds like it has merit. When I thought about specters, I wasn't thinking about Griffith's ability to manipulate souls. Maybe Elfhelm has been keeping a well of them from moving on (maybe those old man trees?) and when Griffith called them up, they were pulled from deep underground, ripping everything in their path.I like the idea that the flipside to Griffith's departed-loved-one lightshow after battles is that it also implies he controls the souls of the damned and can summon them like a plague. Could be a lot of things, though!
Whatever they are, them rising to the surface seems to have either triggered OR was triggered by the breaking of the island's protections.