He told his friend about the game. I don’t think he would have done so if he copied or felt he had “stolen” anything. If he remade the game with this own code and assets then he put a lot of work into it and he can be proud of that (and telling his friend shows that he was). Comparing the game, i do think the clone is better made / more polished. So he really like the game and made a better version of it. I don’t think that’s a bad thing. IP has to be respected (can’t just copy assets or code) but if that’s the case then anything goes and that’s a good thing, it gives us better games.
Think PalWorld, for example, Nintendo, one of the most copyright abusing companies in the world, doesn’t sue them and it’s arguably a better game than anything Nintendo has come up with recently (no new / modern / good / 3D Pokemon games).
Just restrict network access (both in and out) with proper (trusted) hardware firewall. It’s much safer that relying on disabling / configuring etc. You can’t attack what you can’t reach (directly or in reverse).