This is what happens when you habitually work hundred plus hour weeks and perhaps get only five hours sleep a night. There's little to no method to his madness at this point.
Something very similar is also written in Cal Newport's Deep Work book, where Jack Dorsey's typical day is outlined just as a series of interruptions.
I guess that tweeting between these interactions is not that time-consuming for him, + he actually sleeps at the workplace and is 100% focused on work.