No way of knowing the full story, but this is most unfortunate for Moon+ Reader's developer. If Google really did take him down without investigation, he has good reason to be upset.
He's posting new free and paid versions on his site. But if you buy on his site, Google Play updates won't work when he's back up again. He says he'd refund your PayPal payment when you're able to buy again on Google Play, a hassle for all involved.
Too bad. I hope this reader's back up again soon. I prefer it to the others I've tried.