I personally didn't know this, but I also don't submit PRs on github since a while ago.
From the FAQ on https://hacktoberfest.com/ :
> Do I still submit pull requests to earn swag?
> Pull requests and merge requests will no longer count toward Hacktoberfest rewards. It’s easier than ever to submit low-effort spam PRs to projects, so we’re listening to maintainer feedback and no longer actively incentivizing PRs. That being said, we certainly still encourage you to work on open source and share your work with the world during Hacktoberfest. Our new format focuses on learning and building together while reducing the burden of low-effort contributions on maintainers.