I would say he had Serbian origin or lived in Serbia.
Possibly or he was like my old man, a history nut!
I think it is more likely that he studied the history of every major battle between European and Muslim armies.
"Both armies were broken by the battle. Both leaders Lazar and Murad lost their lives, and the remnants of their armies retreated from the battlefield. Murad's son Bayezid strangled his younger brother Yakub Çelebi upon hearing that their father had died, thus becoming the sole heir to the Ottoman throne."
I like history. He knew history, (don't know to what degree), but that doesn't matter, but that is no reason to murder anyone. Murder is very wrong,