Wait, I thought the alleged urination was because he had a stain on his pants, which would imply that his urination wasn't exposing his genitalia in the first place.
@Matthew D: The training division report does, in fact, say that Humphreys "noticed a fresh wet outline on the rear and mid to upper thigh of Mr. Chasse's pants which led him to believe that Mr. Chasse had urinated on himself." As far as I know, the officers said nothing about Chasse exposing himself. Nonetheless, the commander says that indecent exposure was a valid reason for a pretext stop.