I hope you reported the app. That is terrible. If the reviewer loaded and tested the basic functioning of the app, how did that not get seen?
How do you report an App to Apple? Not on the App Store anyway.
I can think of a very simple way to hide this from App Review.
Get the App to "phone home" on launch over the 'net and retrieve a meta file telling it how to behave.
When waiting for review the meta tells the app to do nothing naughty. After review the meta is changed and it behaves badly for everyone else. Bonus - word gets out and you expect Apple to come knocking. You update the meta again and play innocent. "Who us? Nah....".
Epic got away with it until they got caught but that was staged and they came looking for a fight.
These guys must surely expect to get treated no differently, why take such a risk?