I'm perplexed by the author's perplexity. Isn't it obvious that short sayings like this (and other similar things, e.g. children's playground rhymes) propagate orally?
> 6344. You are quite right; it is No. 23 door? - We used to call it the skidoo door, on account of the number. That is how I remember the number.
6345. (The Commissioner.) I do not understand that? - It is an American joke.
6346. Will you explain it? - I could not explain it, my Lord.
It's certain that they propagate orally, but it's an open question of why some things propagate and others don't. Just what is it that took one phrase from that poem and turned into into an increasingly elaborate set of semi-codified structures? The oral transmission puts limits on how fast and under what circumstances it can spread: it requires direct person-to-person contact rather than broadcast.
It's the tip of a ton of research that they only alluded to, and would be curious to know more.
Though, my curiosity in meme propagation is preempted by the curious rejection of memetics as explanation for social or psychological phenomena outside of its adherents.