I get that you cannot label transit as a public good in economic terms.
Nobody who is presenting reasons it should be free or heavily subsidized is attempting to do so. They are presenting arguments about environment, equity, etc. They are not trying to prove that it is nonexcludable and nonrival.
The article even admits that advocates are arguing that it should be a public good by design.
But they are mislabeling it according to economic theory. Who cares (other than academic economists)? In a political environment, where you are talking to other politicians and the broader public, the commonly held version of “public good” seems to fit.
Nothing about this article substantiates it’s core claim: “Mistaken assumptions about public goods pose a growing risk to sound transit policy.”