It comes down to the mechanism by which the zinc oxide acts. If it acts primarily as a barrier to stop bacteria passing or skin being scratched, then it is a medical device. However, if it has a pharmacological action then it is a medicine. If it does both (barrier and pharacological actions) then it is a medicine.
So you woulkd need to look carefuly at the indications, claims, etc of the product to determine the primary action.
It could only be Class 1 if it acted as a bandage and had no medicinal action whatsoever.
Chris