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: Napoli was the better side by chances too.
Napoli: −1.8 for the season (9 in the table). Bologna: −6.0 (18). The gap between points and xPTS is built from matches like this one.