I'm pretty sure that was referring to the fact that the more chests you open, the higher in the loot pool you go.
So, someone who only spends gold earned in-game buys a bunch of chests (and/or also opens all treasure room chests).
Another person does the same, but then also circumvents the system by purchasing platinum (thus, skipping extra in-game time earning gold), and buys a bunch of chests. They are, logically, going to potentially rise higher in the loot pool because if both people play the same amount of game-time, but one also purchases platinum while the other doesn't, then the one buying platinum will have opened more chests in the same amount of time. In theory as a very simple example, not accounting for speedrunning, etc.
I do not think the statement was intended to say those buying chests with platinum would rise higher in the loot pool just by virtue of spending platinum. If that is the case, THEN WHERE IS MY GODDAMN SUPERB HOK RING???
(Last sentence was mostly in jest, not actual anger. Mostly.)