If this post had been written by an anonymous dev, it would not be read as "full of himself". I think the "full of himself" subtext comes from the readers, not the writer.
This doesn't stop the possibility that Zuck actually is full of himself.
It's as much how it is written as it is what is written. No-one who isn't a captain of industry could write a blog post like that, because they wouldn't be writing a puff-piece and write in the guarded lofty tones of political speak.
You can give an anonymous dev the benefit of the doubt that they are probably not expecting millions of people to be influenced by the bullshit they are saying.
This doesn't stop the possibility that Zuck actually is full of himself.