It seems to me at least that it comes through in general executive (dys-)function.
I often can't pay attention to what I want to, even if it is incredibly important, and I care a ton about it. Decision making is awful, except under very specific circumstances: everything on fire at work and you need a solution yesterday? Done. I've got the solution and handed out roles, fires out. I need to eat something and there's a fridge full of food? I will stand there with the door open till it spoils.
I have a very important thing at work that needs to be done and should only take an hour or two? This documentation I've been thinking about writing for three years that noone else asked for has finally found its time in the sun!
Gotta make a phone call for literally anything? Huh, my battery's completely drained because I watched 736 YouTube shorts in a row that I couldn't enjoy because of the pit in my stomach about a friendly 30 second call to the pharmacy.
Anyone can learn to code well enough for a corporate environment.
As the repo owner, you can put in place PR guardrails to help you manage the workload it puts on you. You can enforce pre-commit linting and code formatting, mandatory PR templates, size limits on PRs, etc and these can limit the chunks of work you're sent by this person.
This is part of creating a culture of good code, enforcing code standards and contribution behaviors comes with the territory as you move up the chain in your career.
Another part unfortunately, even if you're not a supervisor is having sometimes tough conversations with contributors it's just part of the deal.
"Hey Bob, I just wanted to connect with you. It seems like you're having kind of a tough time keeping up with our standards (producing code that's usable for our team, or something said tactfully like that), is there something more that I can do to help you? Or is there something specific you're having trouble with? I just want to help you be the most successful that you can be, because the more successful you are, the more successful our team as a whole is."
If you have a discussion or two like this and it's not working out, then maybe you need to talk to Bob's supervisor/manager directly about the issue. Sometimes people don't even realize what's going on.