Because he is a highlander, and it is 100-some years before sajkaca was first worn by the WW1 soldiers, becoming part of the national attire of the šumadians.

Ah, cheers. So what was the common headgear in Serbia back then?

Going off-topic. Since it was the Ottoman empire, Turkish attire was common, headgear like fezes and similar. Serbs also worn šubaras (fur hats), highlanders besides that also montenegrin caps, or other highland attire like skullcaps. Albanians lived in close proximity so their attire resembled that of the other highland folk.