The title is slightly inaccurate / misleading. He quit his job and now runs his own business together with his girlfriend (i.e. they both work). Her part in this is not negligible, perhaps she is the main asset of the company.
(I don't know why this gets modded down, but let me clarify: his old salary is his personal income. The "doubled" salary is the income from his business, apparently the combined salary of both of them - so it's misleading to say that he "doubled his salary")
Your point about having his girlfriend's labor as a huge contribution to his venture is pretty correct. I don't think it down plays his success at all... but it's certainly a significant contributor. If my wife would embrace my madcap ideas and work on them full-force, it would be quite awesome.
(I don't know why this gets modded down, but let me clarify: his old salary is his personal income. The "doubled" salary is the income from his business, apparently the combined salary of both of them - so it's misleading to say that he "doubled his salary")