Agreed with the +1 to Slim,

Not exactly appropriate to just leave your bike lying around the store, wheel it with you if you go inside. On the other hand the employee was acting like a complete j@ack*** doing what he did. Moving somone's stuff and then stalking someone and saying "Are you looking for something?" basically is just antagonization. Respectful thing for the employee would be for him to come up and kindly ask if it was your bike, and if it is then ask you to remove it from the lane.