“In the 21st century, Karl Marx is probably the most famous critic of political economy, with his three volume magnum opus Capital: A Critique of Political Economy as one of his most famous books.”
Political economy as an area of inquiry took off in the late 18th century--in no small part due to Adam Smith--and was already very well established before Marx was born [1]. Absent evidence to the contrary it seems questionable to assert that Marx's use of the term was anything other than the common use of the time.
[1] https://books.google.com/ngrams/graph?content=political+econ...