[Orcrist]

I think what Tolkien means is that hobbits have the ability to not be seen by people they do not want to be seen by(The Big People) They can't really become invisible, unless they put on the Ring. The Ring makes them invisible to everybody. Their art would not allow them to not be seen by everyone in a large crowd, whereas the Ring would. Aragorn points out this difference in FOTR. He says, "I can avoid being seen when I wish, but to disappear entirely, that is a rare gift." This shows the difference between the Ring and the art of the hobbits.