Lucky that he made a product that millions of people were willing to pay hard cash for? Luck is a funny word, and it can be used to dismiss people's sacrifices and hard work too easily.
If I plunk down 1 dollar to buy a lottery ticket and I win the jackpot, that's very lucky. Sure, I sacrificed a dollar, but that has very little impact on me. The risk is low. If, however, I plunk down a couple million dollars to buy lottery tickets and I win, it's less lucky because my chances of winning are greater and of course my risk is much higher.
In spending his time working on Minecraft when he could have been doing any other number of things he was putting the equivalent of the amount of money he could make working for someone else down on the table as stakes. Sure, there's an element of luck, but it doesn't mean he doesn't deserve to reap the benefits of his risk having paid off.
Games are incredibly unpredictable. Even after Minecraft blew up in popularity, there were tons of risks. Plenty of games have blown up, only to fall off in popularity quickly. Minecraft has been far stickier than most games, which is an easy thing to acknowledge in hindsight, but a pretty challenging thing to predict.
1. My understanding is that by the time Minecraft _utterly_ blew up they had a full fledged company going. Some people were probably there from the "a million or two" to "hundreds of millions" of dollars transition.
2. Notch didn't really have a lot of risk going. He wrote a game and it blew up and he hired people off the preorders.
3. Notch got lucky. It's not clear that he's an especially savvy business person, or manager, or etc. He owned most of the IP, but… he had an idea that was waiting to happen, and then it went supernova and infected the minds of most children in the western hemisphere.
If you sacrificed nights and weekends to get the thing to ship, and massaged it into production, and wrote most of the code, and strung most of the deals together, and basically made it work beyond a crashy demo… and it was all just dumb luck anyways, I think it's perfectly natural, human reaction to be resentful that your boss made an insane killing when he rage quit and didn't share much of it.
¯\_(ツ)_/¯ tricky to navigate