I've seen people make video games using a plethora of tools. There's Unity, Unreal, Twine, Flash, etc. But this is probably the first time I've seen someone use Twitter as their engine of choice.
Essentially, the way it works is that Leon (self described as: someone who makes pixel art and posts it online) created a bunch of different Twitter accounts with one tweet and a .gif that tells the next part of the story.
So, most screens look like the one above. You'll have your description in the .gif a long with a little cute pixelated bird doing something cute or not cute. It doesn't really matter. This game has a lot of charm to it and it kind of amazes me that adventure games I used to play as a kid have evolved into this.
If you decide to play it, start here and pay special attention to the display names of each Twitter account. I couldn't help but smile/laugh to myself silently any time I moved through the game. I don't really know what the endgame looks like (I felt compelled to share this with all of you) so I can't really tell you what to expect other than a lot of silly humor and cute pixel birds.