Just because something is free, it doesn’t make it common property. Being able to use the kernel and modify _your own copy_ is not the same as the kernel itself being common property. The four freedoms don’t grant us permission or rights to alter other people’s copies of the software, so those copies are not common property.
> The maintainer didn't have to accept the patch per se. He could have just written "This bug is discovered, dissected and fixed by $THE_PERSON. Patch is implemented and committed by me. Thanks a lot, $THE_PERSON!".
That’s basically what happened, yeah? The author got credit for reporting it.