The opening section quotes an anecdote about Hawking referring to his chances of winning a Nobel:
"Most doubtless saw this as an example of Hawking’s famous wit. But in truth it gives a clue to the physicist’s elusive character: shamelessly self-promoting to the point of arrogance, and heedless of what others might think."
Or, more likely, given the context - he was actually being funny and poking fun at his own reputation, as it appears.