Speaking as a game developer, this is remarkably bad advice for a young gamedev to follow. It doesn't matter whether or not they're "his". It matters that he continues creating. That's the most important thing. He's not making money off of other people's work. He's building a skillset that will serve him for a lifetime. Wasting time fitting society's arbitrary moral standard is time not spent becoming a better gamedev.
Even if he's served with a DCMA takedown notice for some of his apps, it doesn't matter even slightly, because the app isn't the end goal. Talent is. And the way to foster talent is to not stop working.
I'd encourage him to pursue art if he wants to, as it's also a skill which will serve him the rest of his life -- the creators of Minecraft, Super Meat Boy, and World of Goo were all artist-programmers, which seems more than a coincidence -- but it's not a requirement to be a gamedev.