Well, to me, as an archaeologist, an artifact is something made or intentionally modified by human hands. Doesn't matter where you find it. It's a specific term for a very large category of objects. And it's one of those terms that's really of use only to the people who actually need it. Others will tend to misuse it. I think this is true of a lot of words, no? Some people distinguish between bees and wasps; others call them all bees, much to the apiarists annoyance. Some people distinguish between apes and monkeys, others don't. And so on ad infinitum.