Disagree, it has been 'a thing'. Both music and film use the term 'master' for production and release. One would make new releases/mixes from masters. Much like one may branch with a repository.
Now, I'll entertain conspiracy for just a moment. There might be concerning roots here with property or ownership... but if that's the case, the problem isn't with the language being descriptive of the system in which it operates.
We won't 'kill all masters' by getting rid of the word. My real conspiracy theory is this is one of many attempts to sow division. Nation-state nonsense.
Having been in the TV industry as well, it would be virtually impossible to "root out" the word "master" by any woke movement. The word is deeply entrenched there. It's everywhere. I was a little surprised when it showed up as a branch name, however.
Note that there is another instance where this is used much more explicitly with "master-slave" replication. Most people don't even pause to think about that.