Actually it is the pre-war bosnian former yugoslavian socialist flag which has its origins in the socialist communist movement
https://en.wikipedia.org/wiki/Socialist_Republic_of_Bosnia_and_Herzegovina
The official former yugoslavian flag was the star with gold border and blue on top, white in middle and red on bottom stripes. There were a few party variations too, such as the hammer and sickle. I know because I was in Former Yugoslavia before Bosnia became an official independent country.
Regardless, a Muslim has no business in being a nationalist, and all these made up flags are meaningless. This holds true for all Muslims not just Bosnians. Your mentality is not exclusive to Bosnians, it's exclusive to everyone around the world. Nationalism divides us it doesn't unite us.
Former Yugoslavian nationalism and patriotism 'united' people upon the pride of a nation, while erasing religious and ethnic backgrounds (trying to).
Uniting upon Islam is better for us as Muslims, because it too eradicates all preferences and prides of race, nationhood, ethnicity, tribe and cultural dominance. Islam united us through Allah and Islam. Uniting upon anything other than Islam is bound to always fail. Socialist communist and former Yugoslavia failed. Nationalism has failed.
Those Bosnians who still hold onto these old and fabled national prides have only compromised their deen to appease serbs and croats in the process losing their own religion or watering down the religion to please others.