FUSHUFURU
The Grendels came from the island closest to hell. There NORG was leveling up and captured a few of them. When the Grendels came with NORG back to the garden the monsters from all around joined in to fight on the day squall and friends came back from the desert prison.
Marcus
"No cloud, no squall shall hinder us!" - FF9
Games completed - 1,2,3,4,5,6,7,8,9,10, 10-2, 12, 13, 13-2, 13-3 Tactics, Tactics Advanced, Crisis Core, Dirge of Cerberus, KH, KH2, And played 11.
NORG is what almost ruined the story for you? That's it?
Sorry, couldn't resist. Ignoring criticisms of FFVIII's plot, I never really paid so much attention to the fact that non-training center monsters were present to really care. It didn't exactly seem like an issue to me. I think there are far better things to consider when asking, "What the hell were the writers thinking?!"