Yes and no. The idea is that the MTA is claiming that it must be derived from their map, since its style is so similar; by showing there were similar maps made before, the argument becomes less credible.

The point is that "prior art" is a term of art, unapplicable to copyright.

In fact, all IP is quite different, to the point that even calling it "IP" leads to a lot of confusion thinking that it's at all similar.

Obligatory Stallman essay: “Did You Say “Intellectual Property”? It's a Seductive Mirage” https://www.gnu.org/philosophy/not-ipr.html