Explanation ? :
This is an.. alternative reality. One that could have been, but did not happen. Sam has been possessed by Lucifer and humanity has been turned into... let's say, zombies. Angels left and Castiel became human. They're in a small group of humans who are trying to survive and save the world, or what's left of it.
In 2009, Dean time travels to 2014 and witness this awful future. This little comic, though, happens before Dean's time travel ! I couldn't be there when Dean visits from the past, since uh, I've been killed in 2012 (more about that later). So that's uh.. obviously before I died xDD
And if you think that's sad, don't worry, this future never happens. It's just a good excuse for me to draw some silly stuff about our relationship in this post apocalyptic world and have some fun ! And I think I succeeded cause I had a lot of fun drawing this !
