It means we won games we weren't expected to win based on our bad rating (i.e. beat teams ranked better in KP). Another explanation for what KP calls "luck" or lucky wins, is that we're underrated based on efficiency/margin sinking the ship and it's not actually luck, it's that we're better than the rankings suggest. "Luck, which is the deviation in winning percentage between a team’s actual record and their expected record using the correlated gaussian method. The luck factor has nothing to do with the rating calculation, but a team that is very lucky (positive numbers) will tend to be rated lower by my system than their record would suggest."