No, GitHub never required your code to be open-source. In the past, free accounts couldn’t create private repositories. Nowadays, they can, but those private repositories are limited.

A public repository does not need to contain open-source code, or even any code at all. I imagine the repo just contained a README, and that’s completely fine GitHub-wise — why would GitHub mandate people to have code in repos?

Github changed their pricing model last year. Everybody, individuals or companies, can have unlimited private and public repositories.

I have a college student pro account, for free, so yeah :)