@sjw Painting a mural on each corner of a 15 floor skyscraper means 60 murals. If you had to pull that off in one night you'd want about as many people. This would require a bunch of support staff as well, like guys on phones wrangling 60 artists (notoriously erratic people to handle) and a bunch of guys on lookout reporting back to the leaders if the cops or building security show up.
It's a pretty impressive level of organisation. I imagine there has to be money behind this.