I think you are correct. https://news.ycombinator.com/item?id=33990413 From the headscale commit log, seems like it was https://github.com/kradalby not the owner of the headscale repo. And he is making a lot of commits.

So, looks like Tailscale is paying one of the developers to develop for headscale, as par of his job.

This is one of the best ways a company can support an open source project though.