Yeah it's a stupidly good deal from the looks of it. It's very cool of them to resist the industry trend of trying to squeeze recurring revenue out of every product!
How can they even afford doing this?
Quantity, presumably. Procreate itself ist eben cheaper (or at least it was when I bought it) so the model must be working for them. And I'm the perfect example why: I'm not an artist, I barely draw, but I bought Procreate. Why? Because it's a really cool tech demo for that expensive new iPad Pro and at €10 one-time it was extremely easy to justify, even if I've only played with it a bit. I imagine a lot of people fall in the same category and bought it even if they're not the typical market for digital art apps.