I don't see why it would matter, just because you release something under a free license doesn't mean you should accept contributions.

Otherwise all our software would be capable of reading email.

Too late, Bot Builder reads email now

That's precisely why hellcow distinguished between "you can read the source" and "open-source". It's not just a legal difference.

If the license allows you to freely read, modify, and distribute the source, it's open source. If we add "upstream welcomes your contributions" as another criterion, that would disqualify a lot of open source projects including all of the abandoned projects out there.

The Linux kernel is most certainly open source but their criteria to accept contributions is no more open than this or many other projects.

The maintainer(s) get(s) PR approval. Big features that change the direction of the tool are welcome in forks but require maintainers to agree if merged upstream.