It probably all depends upon where it was found, If it was found in a creek or river with lots of other well worn and rounded natural rocks, then that is probably all it is. If it was found on a pre-historic artifact site, where naturally worn and rounded rocks would not end up at due to geological processes, then it is probably an artifact /tool. It does not look to have been shaped by humans into its present form, but if a pre-historic person found it in a creek and thought it would make a good tool as found, and took it with them back to their camp and used it, then technically it would be an artifact /tool. My artifact hunting buddy calls those style objects' dog stones".