If the planets remained in conjunction as they went around the Sun, yes. The planets don't wander as though they're attached to the spoke of a wheel though... and as I click through the explainxkcd link, it seems that someone else has pointed that out, albeit in other words.
He’s super smart. I’ve always thought that an idea he has for a comic starts as part of a funny and/or interesting conversation he was having with friends or colleagues. Then later he remembers some of them and makes comics out of them.