The author just wrote that on the website. This what i placed is just a part from the book, theres much more information. I guess i'll have to order that book from USA…
Info about that is either from American archives, or that book i'll quote down here:
1) Book: Eterovich, Adam S. "Croatian Confederate Soldiers, Civil War, 1861-1865." Zajednicar, May 6, 1970.
2) Archive military documentation:
National Archives. Confederate States, 1862- 1865. (George Petrovich Service Record.)
Austrian Guards. 4th Regiment, European Brigade, Louisiana Militia.
Cognovich's Company. 4th Regiment, Louisiana Volunteers.
Slavonian Rifles. Infantry Battalion, Louisiana Legion, Louisiana Volunteers.
Slavonian Rifles. 1st Company E, Cazadores Espanoles Regt., Louisiana Militia.
Slavonian Rifles. 2nd Company, Cazadores Espanoles Regt., Louisiana Militia.