The census takers (or their supervisors) did not accurately report where you were born, if it did not politically exist any longer. I have seen entries that said "Moravia" which was crossed out and Austria written over -- in a different hand, so I assume it was a supervisor "correcting" the entry. After 1919, "Czechoslovakia" was written in when the real birthplace was Bohemia. So we can assume that George Fenic was born in the geo-political area that was Yugoslavia's boundaries in 1940.
I once did some research for someone, and his grandmother's birthplace changed every census. Then I looked at history, and it was that little part of Poland that changed hands about 3 times from 1880 to 1920, and it then made sense.
According to http://www.infoplease.com/spot/yugotimeline1.html
the name Yugoslavia started being used in 1929.