I think firing without giving warnings and opportunity to improve is sick. These people don't even know they were doing badly. I can't tell if they've been told where they screwed up. These people could be spending a lot of time figuring out what went wrong when everything seemed to be going fine. They don't deserve that, regardless of performance.
They are people, they have lives and it wasn't anything like gross misconduct.
I think Mr Musk has a lot to answer for.