I mean, this entire jaunt was him metagaming so the party could have some fun with all the legendary gear he knew the locations of. It’s a case where they basically shrugged and decided to fully indulge in the power fantasy aspects of the campaign and punch well above their weight class via a collectively overpowered arsenal and OOC knowledge/strategies rather than fudging the dice rolls.

And honestly, I don’t hold that against them. Obviously it’s not good for general play, but sometimes it’s nice to have a sandbox-y oneshot and see the party power through and overcome conflicts that ordinarily would be impossible for them.