It’s a recognised hiking route, they will have pretty much followed this:
https://peaksofthebalkans.com/
I’ve walked one section of the route in the opposite direction, Valbone to Teth, and spent most of the day wondering if sections “would go” on a bike.
Thanks Singletrack for the excellent article, my limited experience in the region echoes a lot of Jerome’s sentiments and reading it brought up some of my favourite memories! Such as being chased by a pack of pigs and drinking raki in a saloon with horses with chainsaws in their saddle bags tied up outside!