I had always presumed that these things were designed by computer. Perhaps they put in some of the seats as a guide. This is a professional seating company who have done bigger contracts that the Amex, in spite of what my eyes are telling me, I find it difficult to believe they are making it up as they go along. It certainly looks like it though.
Never mind - however they do it, they are heroes
It's probably a bit more tricky when you are on the ground doing it - it looks easier from far away. Maybe they just layed out all the blues seat first so they could check they were all spaced out correctly? Maybe the kiddy fixing them in just got a bit carried away and fixed in a few more than he had to? Better they make sure it's right now and so people can see what it looks like in place, and then alter the design if it looks a bit wrong.