This has already been discussed to death. Yes, it’s legal because of the license for this content. No, it’s not ethical. Especially since the “developer” has filled the application description with completely irrelevant game titles in a search trolling attempt.
Using Unity assets as part of your own creation is what they are intended for, I would say. That’s no different than buying models on Turbosquid or whatever. But just opening a demo, hitting “build”, and then claiming the result as your own app and uploading it (and especially charging for it) is what’s unethical. Taking a quick look at “other apps by” on iTunes, I see this particular dev seems to specialize in 99 cent shovelware garbage, so the lack of ethics isn’t really a surprise.