Is your character a magic user/otherwise magical in some way?: Not...technically. He has abilities that seem like magic but are actually technologically based. He does, however, have a natural psychic connection to an 'artifact of God' that causes him to radiate a distinctive energy wavelength.
If yes, can Artemis "sense" this?: 'Divine' wavelength is a definite yes, sufficiently advanced technology is fine if it would make sense for him to be able to feel the energy from that even if it's not actually supernatural in nature.
If yes, is there any specific impression that he would get from them?: The 'divine' wavelength is the sort of thing that drives ordinary humans insane if they came into contact with a strong enough source of it, but his is more or less trace and isn't even noticeable without tuned senses. If he can sense the not!magic, it's very powerful fire, lightning and raw physical enhancements.
Anything else?: Yeah, God is a horribly alien non-hostile eldritch energy being in his universe.