Handicap Results: What does 5.5 handicap driving mean?

The answer is that handicaps are based on strokes gained per shot, not strokes gained per round. For example, if there was a category of 70-80 yard sand shots, a player could have a terrible SG per shot (high handicap) but with 1 shot every few rounds, it doesn’t much impact strokes gained per round.
“Weird” results like the ones you attached tend not to happen on reports with several rounds.