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.
Osasuna created more (1.64 xG against 1.60) and left with nothing.
Alavés: −0.5 for the season (6 in the table). Osasuna: −1.1 (13). The gap between points and xPTS is built from matches like this one.