I see most of the TV Series in the US and it has fairly common to hear a reference to Bulgaria. There are two main reasons:

150,000 Bulgarians now live in the US, if not more.
In Los Angeles there are many who work for the studios for movies etc, as actors or programmers for CGI movies.

I don't know if you are aware that the wife of Tom Hanks is Bulgarian. Also there are plenty of movies being filmed here in Bulgaria for global/us markets and these big Hollywood stars talk to people about their experience in Bulgaria. I have seen in at least 10 times on Leno/Letterman.

So there are plenty of people involved in the business that sooner or later a Bulgarian this and that would creep in to the picture.

Not to mention that for Americans anything foreign is funny, it ain't like the good 'ol US of A, that Tambuktu - a made up place in the universe, and shit like that which is all GREEK to them.

http://www.youtube.com/watch?v=jxTUHCCjJm8