All of needs is a qualifier. “Permanent” or some appropriate synonym would work. Also, “structure” is probably technically true, but not colloquially, common-usage true.

But: it’s a comic. XKCD’s main failing is that it’s mostly a serious, science-based unless it’s being outright silly, which triggers the pendant in us. Or, in some of us. My defense mechanism is that Randall is far, far more educated about these things, and I immediately fell stupid for being pedantic; like how you might feel when you find yourself criticizing the phrasing of a sentance in “On the Electrodynamics of Moving Bodies”.