I'm not the parent, but I've been burned in the same way. In an ideal world, yes - that would be the right way to handle the situation. In a company you'd want to do that, and probably give the programmer a mentor who can do code reviews and whatnot.
Unfortunately thats:
- Thats a complicated conversation to have at the best of times. With volunteers over the internet its much harder to organise 1-on-1s.
- A huge time sink. Usually I could make the changes themselves in less time than it would take me to explain the changes to a junior developer. Its especially hard to justify for projects I have in maintenance mode, where I don't want to spend time working on project features at all. Long term hopefully the time investment will pay off, but they'll probably disappear long before then.
- Honestly, its also not that much fun. I contribute to opensource projects because I like making things. Managing people doesn't rub that itch.
I'm not saying I have a better solution. But faced with a stream of mediocre PRs from an enthusiastic new contributor that you don't have time to review, what do you do? Abandoning the project to the new contributor sounds pretty reasonable to me.