Maybe i misunderstand his words. But i'm asking because i play that chapter and as i know from experience and only, 99% of the times the 8th is the glden one (for the story line dungeons), and always u have to spin a lot of times to get the 8th one ONLY if it gonna be golden. If its brown u get it easy with a few spins.
I notice that if u finish the stage without taking the 8th (golden chest), the next run its all 9 brown again and agaian and again .... Until after 20-30 runs you have diifficulties to take the 8th chest.... If u lucky and you didnt kill the opponent u get it. If kill them quickly tou get a brown one just for the +1 chest at the end.
The chests that may drop are calculated at random when the chapter is loaded as you enter it. If the max number of chests is 8 it can be 7 brown and 1 gold for example (or 8-0, 6-2 etc, at random). Then during the chapter the drop time for brown chests is much lower than gold chests (from my experience). If you get very far in the chapter and you still have one more chest left to drop, chances are it's going to be a gold chest, as otherwise it would've already dropped.