The original video is of Split, Croatia. Which is way cooler than Baldur's Gate as the medieval city was built on the floor-plan of Roman emperor Diocletian's "retirement" palace.
Split is awesome. It’s probably not quite as spectacular as Dubrovnik, but inside the walls Dubrovnik is a bit like Venice, where it is (or rather was) full of tourists and with everything geared towards tourists. Split is much more a regular town. You can go to a bar and meet actual Croatians. Visit both though when the current bag of shite situation is under control. 2020 sucks.
I suppose that the former developers had those pictures, when they made Baldur's Gate 1. Hard to know now, the game is old. Sadly, there is not making of, or interviews.