I think when discussing his statistics it's important to keep in mind that he's only been a pro for 4 months. And that he isn't at a top club that regularly dominates possession, features intricate link up play between its forwards or a roster stocked with world class players, etc. He's an inexperienced 18 year old developing in the most defensive of Europe's top leagues, for a club unaccustomed to talents of his quality.
He see's runs and plays passes that if he were at Barcelona would be met by a player at the other end that could finish or continue the build up, but at Rennes, ends up intercepted, turned over, or recycled because most of his teammates lack the quality to take advantage of the chances he creates. Even so, there's no mistaking the quality of both his passing and his vision.
Compared to the forwards he plays with, Giovanni Soto & Paul Georges-Step:
Ntep - 3 assist / 1.5 KeyP / 24 AvgP / 72 PS% / 1.2 crosses
Sio - 5 assist / .7 KeyP / 20.3 AvgP / 75 PS% / 0 crosses
Dembele - 4 assist / 1.7 KeyP / 20.9 AvgP / 70.7 PS% / .9 crosses
And his passing metrics don't appear so poor.