Ratings are not based so much off of stat lines as they are off of the players actual skills and GS, which impacts the game. A player with a 30k salary will almost always have a higher Game rating than another player with a 3k-4k salary like your guy, even if your guy has a 50 point game and a triple double.
Murray/Harris/MPJ/Grant/Jokic - 2020 NBA Champs