Earlier quoted context omitted.
When every user is limited to updating a single pixel every few minutes, how else could any group of mere mortals create and maintain such a large picture of the Mona Lisa? It's not visually easy to see vandalism on such a complex construct, so expecting that mere people were able to almost instantly identify and fix graffiti is folly. And that's just one highly complex piece which evaded defacement.
Well it's actually pretty simple. They created grids and coordinate numbers that told the groups what each and every pixel should be colored. Then all anyone that wanted to "help" had to do was just look at the grid, and pick a pixel that was wrong to fix. Like you said, each user had plenty of time in between pixel placements to look at the map and choose their next "fix".
Because the way the US flag appeared certainly looks artificial.