Your post led me to install your app and play through 10 puzzles. The post doesn’t even show the app!

What’s the name for this sort of marketing?

I really like the interface you’ve built for completing the puzzles. Very clean - it’s very nice to not be bombarded at every screen.

I'd say "Content marketing" [1]

1. https://en.wikipedia.org/wiki/Content_marketing

Thanks very much - really means a lot that you enjoyed it, we put a lot of effort into making it.

Knowing your audience, and captivating them at grassroot level or in an unexpected place, without making it feel scummy (sometimes)?

Guerrilla marketing.