What does "v'Zeh" come to include?
Targum Yonasan: It comes to include the blood and the skin 1 of Sheratzim.
Why does it say "v'Zeh Lachem ha'Tamei"?
Da'as Zekenim: They are permitted to Nochrim. A parable for this is a doctor who visited two patients. (One of them had no cure, so the doctor put no restrictions on him. The other had a cure, so the doctor restricted his diet.)
Perhaps according to R. Avahu, we would have thought that it is forbidden, if Sheratzim are included in "Lo Sochlu mi'Ma'alei ha'Gerah