That guy completely relied on the financial support of his girlfriend for years. I think he did some odd jobs here and there, but mostly he was just working on the game not making any income. Obviously for that game it paid off in spades, as they were millionaires pretty much overnight once it was released, but that won't be the case for every game, or in fact most games, and it's not something you should ask of your significant other most times.

I've worked on eight titles professionally working for game companies that never made the money spent developing them. It's a hit driven industry and there's no guarantees, unless you hit on an untapped market with a lot of pent up demand for something (like Natsume had been dropping the ball and releasing garbage Harvest Moon sequels for over a decade at that point, Stardew Valley came along and showed them what the fans actually wanted). Even then it's still not a guarantee.

I'm out of the video game industry now, but still work on my own games, but it's only a few hours a week here and there. I've had some success over the years, but not enough to justify asking my wife to let me quit my job and do it full time.