Music from the Earliest Notations to the Sixteenth Century

Voice-exchange over a pes—shades of the Sumer canon! And all the more so if we reflect that a
round, shorn of its mock-imitative beginning, is just a perpetual voice-exchange disguised as a canon.
(Gather three companions and sing “Row, row, row” or “Frère Jacques,” beginning with the fourth entry!)
But the use of an Occitan cantus-firmus tune (as well as the source situation) suggests that this is not an
English piece, but a French one that uses similar devices. Is that an example of English “influence,” then?
Maybe, but why couldn’t the English practice be an example of French “influence”?