The thing with nationalism is that it's any idea that is dominated by simpletons. At least, they make the most noise in the nationalist field.
This kind of argument can be found all over the place. I've heard Germanic nationalists say that the Asian steppe begins in Poland and Poles are a mongoloid horde, yet the same person would them praise Russia and Ukraine. Then you don't have to go very far to hear some Slavic nationalists bash Germanics for being something or other that's intrinsically inferior. Notice that most of these clashes take place between neighboring peoples. Each one views the other as a flawed version of themselves whom they view as perfect. Nationalists will overlook any flaws that they nation may have and say "yeah, well that's the way we are and that's perfect." This also goes for good their nation's good traits and in seeing them as perfect they feel that they are justified in spreading them all over to "help" others. Every empire and former empire is pretty much guilty of this in some way.
My main problem with nationalists is that they, for the sake of superficial pride, refuse to take an honest look at themselves and their own people. Using your quote as an example: are there some Serbs descended from Turkish nobles? Yes, the Ottoman Empire lasted for 500 years. Is the religion of the Bosniaks an indicator that they have Turkish influence? Same answer as above. This is really bullshit reasoning and looking at a few surface traits of a people. Just think: should Christian Slavs be looked down upon as somehow being more loyal to Italy or the Vatican than their own country? Or are Sorbs Slavic traitors for openly accepting Germanic culture and also administration? Those don't even begin to make sense.
These kinds of nationalists look at one picture from their past and say that is exactly how their nation should look now. Meanwhile, time goes ever forward.
These divisions in former Yugoslavia are often driven by such absurd claims that one has to wonder if they are genuine arguments that people have or are intentionally planted discord. People can be very stupid, so I won't rule out the first one, but neither will I rule out the second one.