Manual inspection of todays commits shows that nearly all of them are @chromium.org email addresses, which usually means a google full time engineer. There are some from other companies (microsoft, intel, nvidia). None from random hobbyists that I saw.

OK and that makes perfect sense.

But then saying "therefor other days I expect those other engineers were @chromium", not so much. I expect that the vast majority of contributors are making ~1 commit and then never again.

It also doesn't take into account that the project is over a decade old and many people who have committed to it as FTEs are no longer doing so.