I think you're misunderstanding this rule. If I made a phone game where there was a "store" where I could buy physical stickers but each sticker pack came with a code for 10,000 in-game coins Apple would see that as just a way to get around paying 30% for something digital.
And if the only way to get in-game coins was by buying stickers off-app Apple would say you have to offer buying them in-app too as an IAP.
And if the only way to get in-game coins was by buying stickers off-app Apple would say you have to offer buying them in-app too as an IAP.