Perhaps the parent's use of "contradictory" wasn't so great; I would say "hypocritical" would be better. This isn't about doing anything legal or illegal, or violating or not violating anyone's terms of service. It's simply pointing out that Apple, when given a choice, would rather use an external payment processor (in order to pay lower fees) when building an app for a platform they don't control... while at the same time denying people the ability to do that on their own platform.

To me, that sounds like a compelling argument in a hypothetical anti-trust suit against Apple where a plaintiff is claiming that Apple's requirement to use Apple's in-app payment system for all payments in iOS apps is anti-competitive behavior.