Anyone paying attention to his tweets can tell this is obvious fake front that he tries to maintain (one that actually works on a lot of folks). On some level it's probably technically true part of the time, counting long flights in his private jet as "working", etc.
To be fair, I do think there are people who work hard, especially founders. There are also vocal pretenders like Musk. My guess is that the folks who do work really hard are probably the least likely to go around broadcasting that fact. That was my experience, at least.
I was never VC-backed but I did a couple runs (combination of bootstrapped and angel investment) and I worked like crazy all the time. I never really thought about the amount of work I did until after (I was too busy worried about failing). I never discussed the amount of work I did with anyone, especially not publicly, because I never felt like it was anything to brag about (I still feel this way). This post is probably my first public mention of it TBH. :)
