These stats are simulated by the system. They are still representative of how the player should be expected to perform. The player has been generated with a specific talent for football. Whether you'd buy him on auction from a real club like before the Auction system rework, or from the system as it is now, that player would always have varying football skills. He could be a scrub, he could turn out to be a star in the making or an already proven master of the sport, but you as a Manager would still have to determine this by checking and comparing the information his profile would provide you with.
Winning doesn't mean high player ratings. The guy is new to your team. Play more matches with him in the starting line and see how he averages out. He already has a 7 among those 9s and 10s, so it looks like his performance can fluctuate. Also in order for him to have any chance of raising or going low on his rating, he should be present where the action is during a match. E.g. A defender can go low if he's been constantly assaulted by the opponent's attack and just can't handle it, or vice versa. But if there is little to no action over at your side of the pitch, that same defender may just stay with 6.5 or 7. Unless he helps out with assist during attacks or even scores. I.e. a player has to play in order to gain any alterations to his rating.