The pilot reported that he was attempting a wheel landing in a tailwheel airplane at his private grass air strip. During the landing touchdown, the airplane bounced once, settled back to the runway, and then suddenly nosed forward and came to rest inverted. The pilot reported that he did not know why the airplane nosed over, but suspected the pilot rated passenger in the rear seat may have manipulated the flight controls in some manner. During a postaccident interview, the pilot rated passenger seated in the rear seat stated that he remained clear of the rudder pedals and flight controls for the entire flight. The passenger also reported that he observed the flight controls move abruptly to the full aft position just prior to the nose over. The pilot stated there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation. During a post-flight examination, the rudder and right wing were found to be substantially damaged.