Sorry my sentence was not sufficiently well specified. What about:
“The fact that a language model can reproduce Python strings without any operations that are isomorphic to the production rules in the BNF specification of Python grammar shows that they are not informative about Python grammar.”
Now the contraposition is (I think)
“If a language model is informative about the grammar of Python then it cannot produce Python strings without any operations that are isomorphic to the production rules in the BNF.”
This then becomes the argument about implementational connectionism I made in my longer paper. If the network is implementing the BNF then it becomes far less interesting as a radical new model of Python in this case, but generally as language or cognition.