You made the baseless assumption that the developer of Domina is just a hobbyist and that it is not his main job. That is extremely unlikely and showcases that you have no idea what you are talking about.

I am a game developer, I know my shit. "Making games as a hobby" is a full time job. Yeah sure, they might have an salaried job in addition to their "hobby", but that's more like doing two full time jobs at the same time. GameDev is full of extremely passionate people, some of which are willing to sacrifice their entire free time towards making a game. Those that don't usually don't find success either (excluding some freaky accidents like 2048 and Wordle).

It's definitely this guys main source of income. You don't succeed on Steam unless you make it a full time job.

Your numbers makes no sense

6,000 reviews * 30 sales gives 180,000 sales, so $900,000 earnings, not $35,000

It already made him bank. There are no official sales figures, but you can expect about 30 sales per review, if we only count 6000 reviews before the review bombing and go with $5 per sale then he would already have earned $900k with it. For a game made by a single guy, probably not even commissioned any music or art.