In short, it means that doing things better (e.g. making a piece of software faster) for the sake of things being done better is praised, not tolerated, as is the case in the many "let's just ship it, we'll fix it later" software companies.
> when I see people from inside Twitter correct him on Twitter, with specific technical statements describing what's going on—and then he fires them
As far as I remember, the guy just said something along the lines "as the person who actually works on this, it's not 1000 RPCs.", to which Elon asked for a specific number, the guy replied with vague answers like "it only does like 50 RPCs all of which are async, but the software is full of bloat and various features slowing them down" which sounded nothing like "specific technical statements" to me. But I can't find the Tweet thread right now, so I won't stand by this opinion completely.
Regardless - even assuming the guy is 100% in the right - I don't think that publicly going against your boss in such a passive-aggressive way, at the same time portraying him as "the guy that doesn't know what he's talking about", is a right way of handling false information. Maybe another engineer told him 1000s of RPCs are being made, or he just made a hyperbole for the sake of explanation. Benefit of doubt, and all that.
Being rude will get you fired, no matter how right you are, that's kind of a given.