A save is when a GK prevents a shot on target being a goal (paraphrased). There are also catches, interceptions etc that don't count as saves.

Neither Saves nor Goals Conceded or Clean Sheets define a GK performance.

Other GKs in the game who had 0 saves and no GA will get a different rating.

PS. Its not the ratings that are bust (although they did seem to give a global boost for a win - like feckin fantasy football! grrr) but the stats which describe them.