If the drone was close enough for a decent shot, sounds like it was close enough that it deserved to be shot. If I was out hunting and someone was following me around with a drone ruining my hunt, I expect I'd do the same if it was safe to do so (shotgun, not rifle!).
Hopefully "Norfolk OPP are investigating" means they are investigating into whether the drone was being lawfully operated (i.e. did the operator maintain a line of sight and not fly within 150m of people, animals or builings?). My guess is it was operated well within 150m of a person if it was shot. I'm not sure that that is actually law, but it is listed as something not to do on the Transport Canada website.
-moose