Sounds like your friend should have read the App Store Review Guidelines, the rules are all clearly stated and have been for so many years now that it should come as a surprise to nobody doing business on iOS.
I think this saga proves the rules are not clearly stated. The rules do not make clear at any point that “reader” apps (however Apple chooses it will define them today) and business focussed apps do not need to offer IAP. Apple didn’t even make that clear in their rejection. It took a statement from them to a blog to make it clear.
Actually they don't. If you go look at dhh's twitter thread, he has a table of direct competitors to Hey that don't have iap. Yet they are on the store