Here in the US each state makes their own hunting regulations, and oftentimes, each county within a state will have regulations of their own.
For instance, here in Pennsylvania we don't have a dedicated shotgun season, we have small game season and deer season. Some counties are "shotgun-only" areas for both small game and deer because of housing density in those areas. In my state a fully rifled shotgun is still considered a shotgun regardless of the ammunition used, the logic being that an errant shot with a slug poses a much smaller danger than that of a high-velocity rifle.
I'm unfamiliar with the regulations in the state where the owner of this gun lives.