He learnt the basics of tracking, enough to learn how to avoid being tracked. So he's terrible at tracking, but knows enough to throw off scent trails and cover his tracks. Think of whatever he's tossing on the ground as a Masterwork item giving a circumstance bonus. Hell, whatever he's throwing might even be in one of the Complete splatbooks. There was a ton of stuff for boosting skill checks in an overly specific way (tube of baby rust monsters, anyone?).