Let me preface this by saying I loved this game. The universe is very compelling, and the art, music, story...
Anyway, this isn't the first we've seen of the world shown in this game. There is of course a prequel of sorts, Escaped Chasm, but there's more than that too. Temmie's been giving us little pieces of this world for years now, and it wasn't until Escaped Chasm and Dweller's Empty Path that we finally saw some of the pieces fit together.
If you want to find little tidbits of Temmie's universe, there are art works, short animations, and even some music on her Tumblr, Instagram, Twitter, and YouTube pages. Specifically, Dweller's of the Mountain's Forest, one of her earliest animations, shows a story hinted at directly in this game.
[EDIT: Temmie released an update, and apparently the previously mentioned animation is... well, just read the update]
So far, Temmie has left the story pretty open-ended in each of her games, but I think it's safe to bet that things will make more and more sense as she releases more content.
Please post a comment if you find anything from Temmie that I failed to list above.