It's not because of the range. It's because of the psychological factors of taking a shot in a crowded area, at a human target, and then how the exfil was quickly and skillfully commenced. This was someone ready to do a job and they delivered, then they got out of there. What's more, they had help either intentionally or unintentionally when law enforcement apprehended TWO separate false suspects but the sniper got away. There are too many things wrong about this.
Discussion
Anyone with military or hunting experience is up to that sort of kill, if they want it bad enough. It wasn't some sort of genius act. And, of course, they left. Not every shooter is suicidal.
The people they arrested weren't very sniper-y and didn't have real rifles. Incompetent police are not proof of professional hitman.