These apps do "a bit" more than violate Apple's design guidelines.
For example, one of the apps from the article claims to use 'GPT-4' and they actually do call the OpenAI API, but use the GPT-3.5 model.
Another app that also claims to use GPT-4, actually uses a different (self-hosted?) LLM.
In my opinion, this is a scam - a fraudulent attempt to make a quick profit.