I'm not familiar with OpenAPK, so after taking a look at the main page selected Fennec (Firefox Android).
I know that Fennec releases (usually) are built by F-Droid, so I was interested in how OpenAPK provides the app.
Then a quick look in their FAQ shows:
Q: How do we obtain the apps?
A: At OpenAPK, we curate a comprehensive collection of open-source apps sourced directly from trusted platforms like GitHub and F-Droid. Our aim is to make these applications easily accessible while maintaining transparency and authenticity. Each app listed on OpenAPK includes a link to its official repository, ensuring users can download the latest and previous version straight from the original source.
I guess the above partially answers your question.