Is your character a magic user/otherwise magical in some way?: Yes
If yes, can Artemis "sense" this?: Sure.
If yes, is there any specific impression that he would get from them?: Witch magic is more the capacity to channel life energy than anything else, though some are more adept at this than others. That said, Teravian is the second-most powerful witch in his canon, so there is that.
Anything else?: Not that I can think of.