I understand that. But he said "forever." Twice. As in; eternally, always, and an endless period of time. I was trying to put emphasis on the forever part.
My take on that is that he assumed at the point when banishing them for eternity that the Veil wil solve the issue with them, it was a solution made to last and prevent them from ever wrecking havoc again.
However, waking up few millenia later, he finds out that it isn't happening (the Veil destroyed everything he treasured, and made the world from his perspective a really awful place to live, that's where the vinegar fly lifespan gremlins come in), that his solution wasn't solution at all or at best temporary.
So the banished forever would probably just refer to the punishment he intended for them to endure at the moment of creating the Veil. Which, considering the current events, is not forever anymore, since he wants to back-paddle like an unskilled hunter and tear it down.