I am seeing the mobile version of the website on my desktop

[dmjalund 1,048]

and I don't know why

[Simon 885]

a) your browser is (for whatever reason) identifying itself as a mobile device (this would be part of the user-agent header in requests to the server)
 

b) you are sharing a cache with your mobile device (tricky, but it's been done...and a horrible idea)

 

c) you have happened across a direct link to set the theme (specifically requesting the mobile version) and are using that as a bookmark

[dmjalund 1,048]

none of these things

 

but it's back to normal now

[Simon 885]

One of those things, guaranteed.  You're not special - there's no special code in the site that said "if dmjalund visits, show the mobile version"