YMS

You are right, but for xkcd it’s a concept to have a second joke in the alt text since forever. There used to be a transcript of all comics right on the site available for those that need it, but it has been discontinued, probably in favor of explainxkcd.com, where you’ll still find a transcript for every comic.

In that very toot they literally say they will defederate as soon as there is any reason for it, and they will be watching for such reasons.