It is strange that he had an Italian passport as during that time the Istrian peninsula was under Austro-Hungarian rule (1815 - 1918). Only after WWI the area passed under Italy (1918 - 1945). John A (what is A for?) Ivancic was probably not Italian but spoke Italian (besides his Slovenian or Croatian) ad most of the people of the area did and still do.
My g-grandfather (mother side) was Stefan Ivancic and he also emigrated to US during that time (1903 - 1909). He stayed only for short time and than retourned home (exact dates are mistery).
If you find anything mor specific on John Ivancich I could try to find out something. Are there any towns he mentioned (besides Trieste or Trst, a port in (now) Italy where he probably started his journey to US; names of other relatives in the "old county" etc.