There are many possibilities. Croatians were split in half, one half fought on the German side, the other were partisans. possibility 1: he fought for the Independent State of Croatia (NDH), a German puppet. He was caught by the Yugoslav Army (partisans) at the end of the war, spent some time in the prison where he was branded and then he escaped to the West. I think this is most probable, because if he fought for partisans, he would probably not say he fought for Croatia, but Yugoslavia. Possibility 2: he fought for the partisans, was caught my the NDH forces or the Germans. If he was not Jewish, he would be imprisoned in the NDH prison camps. If he was Jewish, he would end up in the concentration camp. Many Jewish persons decided not to return to Yugoslavia, so maybe he emigrated to the West. But then he would not classified himself as a displaced person. There are many more possibilities, but it's hard to say. Many incarceration systems used tattoos for marking the prisoners.

My grandad's story: he was enlisted in the NDH forces, but he deserted after a year. He spent three years hiding in the village he lived. The policeman, the postman and many other people did not denounce him to the authorities because he had four small children. After the war, the Communists wanted to imprision him for being an enemy soldier. He was saved by his cousin, a lieutenant in the Yugoslav People Army.

If you look at the other, partisan side, there are some interesting situations, like:

1. Communist would join the artisans for ideological reasons. 2) captured NDH soldiers could decide to join them to avoid being imprisoned. 3) Jewish people would join to avoid being deported to the concentration camps. 4) Serbian population would do this to avoid deportation to Serbia or to revenge the atrocities suffered from the Ustashas (radical right nationalists). 5) Left intellectuals who were not Communists also joined them. 6) Dalmatian and Istrian Croats, whose lands were annexed by Italy or were part of Italy even before the war would join the partisans, too. Often these people were devout Catholics. There were even some Catholic as well as Orthodox priests in the partisans. 6) After the fall of Italy, some Italian soldiers joined the partisans, too.

So, neither were all partisans Communists, nor were all NDH soldiers fascists. This traumatic period still marks the lives of Croats, Serbs and other Southern Slavs today.