I might do that hobby far less in free time but it is far better than doing something I hate for a living.
So I guess key point here you need to also be relatively competent and the hobby has to be marketable. I'd be miserable if my ops jobs would just be managing someone's shitty Wordpress instances all day.
As article's author showed being mediocre in market with a lot of competition probably won't get you all that much money, passion or not.
Also, it is sometimes worth to leave the "business" part to someone else and just find a job. I absolutely hate anything around a business so it is fine tradeoff for me to have someone else manage majority of it, find customers etc. rather than be whole one man shop.