My main reasons except of that this guy is just a nit (based on vpip pfr...) is the fact that his natural bluffs are KJs,KTs,T9s,98s,T8s,JTs those all hands are at least gutters which are barreling the flop and turn at really high frequency imo.. only J9s is a possibility which we btw block.. or it might just 3bet preflop..
One thing which makes me wonder if my fold was right or not is the bottom of his vbetting range.. in game, I assigned him KQ being the bottom, so I said to myself that I would call KQ on the river for this reason. Also dont expect that he turns pairs into a bluff.. on the other hand my range might look a bit capped though, but I also have some Axs.. but yeah without folding QJs I am already overfolding.. soo maybe my reasons to go even more exploitable arent good enough.. but I just cant see many natural bluffs in his range as pointed above.. so I am prone to fold in a vacuum vs a reg..

Would you call this river against an unknown reg?