So who sent the package? Where did it come from? How did the courier end up with his own town? What was the courier doing before he ended up with his own town? Where was the courier born?

No one knows. No one knows. No one knows. You decide. You decide.

Well WTF? This was supposed to bring the story 'full circle' and all it did was ask more questions! How do you just end the game saying your character owned a city with no explanation as to how or why he/she has no memory of owning a city? And now some mystery package destroyed our mystery city! WTF?!

No. You weren't the mayor, really, you were just someone people followed in the path of, in particular through what used to be Hopeville and the rest of the Divide. An independent civilization sprung up around the road that only you had the unbridled cojones to walk alone, and one day, you delivered something from the old world, possibly from the Enclave, and just took off before it did what it did. Why you don't put two and two together is... up to you.