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.
The score matched the game: Cagliari was the better side by chances too.
Parma: +0.6 for the season (15 in the table). Cagliari: +6.2 (4). The gap between points and xPTS is built from matches like this one.