@Bugpope
You should go look into the tent to the left of the first stage if you're able to replay the grandfest. You'll see Acht standing outside of it and the inside is literally just Marina's simp tent. There's a bunch of water(?) bottles and only Pearl merch surrounding her laptop it's insane.
I like to think that Marina invited Acht to stay there during the fest and that Acht was very uncomfortable upon seeing the decor but didn't know where else to go so they just stayed there with all the Pearl paraphernalia staring at them.