Graffiti's aren't about necessarily the most skillful plays, but one of the most memorable plays.
Olofmeister's defuse was memorable, it wasn't necessarily skillful because all he did was hold e and the molotov didn't kill him early enough, but it was a crowd-pleaser.
Dosia's grenade was pretty skillful, but it got a graffiti because of how memorable it was to the crowd, and it is one of the most viewed twitch clips of all time.
s1mple's awp play on cache was somewhat skillful, but also mostly luck. (Falling awp shot + a noscope right after from a decent range to win an important 1v2). It was very memorable (crowd pleaser)
Just like the above examples, cold's awp play was very memorable and, in the context of the map, was very important, even if lucky.