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.
Venezia created more (2.44 xG against 1.79) and left with nothing.
Frosinone: +4.8 for the season (6 in the table). Venezia: −5.5 (20). The gap between points and xPTS is built from matches like this one.