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.
Atalanta won against the run of chances: Bologna created more (1.24 xG against 0.18).
Atalanta: +3.3 for the season (11 in the table). Bologna: −6.0 (18). The gap between points and xPTS is built from matches like this one.