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.
A draw, but Brest created more (2.63 xG against 0.77) — points dropped.
Le Mans: +0.8 for the season (9 in the table). Brest: −4.8 (11). The gap between points and xPTS is built from matches like this one.