As for how it’s made:
The game is written in inform 6, which is a programming language made for creating text adventures.
The web-based interpreter is Quixe, which runs ulx compiles of inform/glulx games. (Though Frotz or some other computer/tablet/phone-based interpreter will do a better job and allow for saving your game)
The game itself can be run on other interpreters, which can be installed on Android, iPad, Linux, Windows, Mac, DOS, Apple //e, ZX Spectrum, PalmOS, Blackberry… That’s one of the really awesome things about inform based text adventures, they can run on freaking everything.
There’s a lot of links in that bit of text up there. If you read through a lot of that, and through the DM4 for inform, you’ll know how to write an Infocom style text adventure.