He implies that this happened organically, without paid installs. And his price point is $.99 at the time of this writing. And he doesn't use IAP.
Those are choices he's made that drastically limit the upside he could earn. I respect the hell out of those choices, to be clear. But they are choices.
It's well understood that the way to actually strike gold in mobile gaming these days is to get to a point where you're arbitraging paid installs. You've got IAP hooks up and running, you've got quasi-addictive mechanics dialed in, and your blended CAC is less than your LTV on converted installs. You spend a boatload on installs every week, which are recouped by the revenue you earn from your casuals and especially your whales. Now you're in the shitty IAP/P2W business, alongside everyone else. Now your game kinda sucks. But now you're minting money.
That's pretty much the BigPublisher playbook. Indies can run it, too, albeit only to a point, and with a lot of soul sacrifice.
All of that said and done, I am impressed and inspired by what the author has been able to accomplish organically. And, while his earnings may seem depressing from an outside perspective, they are respectable, and to be respected. If he wants to build a larger business from here, again, he'll have to make some Faustian choices as outlined above. Or he'll need to raise his price points and/or adopt a high/low versioning approach.
This is the way the world is going to work until Apple and Google decide to put the smackdown on paid installs. Which they won't, because their big publishers make them so much money, and their big publishers have optimized a formula reliant on paid installs and drowning out the small guy. (Theoretically, feature placements are supposed to counteract this phenomenon -- but, as the author points out, they accrue most readily to the big publishers, who can afford to invest millions in production values, and whose games are big enough to be itemized on the App Store's monthly earnings statements.)