I've hired many people and interviewed many more.

What possible reason would I have to interview someone if they had neither relevant experience, nor a degree? Should I just ask random people I see on the street to come in for an interview?

If they can write a good covering email, have a few github repos, and some other indications that they might be smart/capable. I know from experience that it is easy to get interviews on that basis.

If you're talking about people who have no experience in the sense that they've never written a line of code, then no, obviously not. But professional experience and relevant qualifications are not necessary.

As with any job application, you need to have something going for you. It just doesn't have to be any of those two things.

No, you ask random people on LinkedIn like every recruiter does.

I used the word 'probably' on purpose.

Ehh, I guess, but lacking relevant qualifications and experience doesn't even make it difficult to get a coding interview. It is no doubt the case that most people being interviewed have relevant qualifications and experience, but that's not because there's all that much of a barrier to people who don't. There is certainly far less of a barrier than there is in academia.