They're likely leveraging a number of guidelines. Primal is multi-platform, and apps that are can let users access content, subscriptions, or features acquired outside the iOS app with the key condition that these items are available for purchase within the iOS app via in-app purchase. Primal frames these as pre-paid zaps, and when you put all that together with a few other guidelines then it's likely they are just taking a savvy approach and it's not Apple misunderstanding what Primal is or does.