Is my internet being piggy backed?

A series of articles on wikipedia have been edited, apparently from this ip address. I have no memory of these edits (indeed I had not even heard of some of the subjects choosen).

How can I find out if this is?

a) an error by Wikipedia
b) someone piggybacking the router

The main router is connected to a mac which runs Snow Leopard. Any help or advice is most welcome.