The score says how it ended. xG says how it should have ended: it is the sum of the chances each shot was worth, not an opinion about the game.
Cagliari won against the run of chances: Udinese created more (1.85 xG against 0.64).
Udinese: −1.0 for the season (13 in the table). Cagliari: +6.2 (4). The gap between points and xPTS is built from matches like this one.