Don't worry about it, it happens a lot, people park their names on Sedo, they sometimes drop and they haven't bothered to remove the domain from their account after it drops, so it'll still be listed for sale on there.
If you send Sedo an email stating you're the new owner of the domain, and that a previous registrant had it listed on their site, and that you don't want it listed on there, they'll remove it.