You are half right, half wrong.

It is true that a non publicly traded firm won’t see an immediate effect if one of the shareholder leave the ship, but businesses work on trust. If Tencent sell its share, it is a sign that it doesn’t trust the studio anymore. Thus, potential private investors, like banks, will be more hesitant to work with them, and will ask for higher rates to compensate for that perceived lose of trust. Thus, hurting the Studio.