They likely mean that theses are the two most prominent free-market schools (at least Chicago once was). But, as you point out, method is crucial. A model is a foundation of sand (as the decline of the Chicago school as a proponent of the free market illustrates) and leaves one open to the charge that one’s economic theory is just a scientific fig leaf for covering up one’s unseemly libertarian prejudice.
Liberty Magazine published a piece on the “Austro-Chicagoan Empire” in 2005:
https://mises.org/journals/liberty/Liberty_Magazine_November_2005.pdf
