It sounds like the effect depends on whether the surrounding airflow is turbulent or laminar. I believe that making an object smaller biases the airflow more to

It sounds like the effect depends on whether the surrounding airflow is turbulent or laminar. I believe that making an object smaller biases the airflow more to turbulence, so ping pong balls and golf balls may be too small to show the negative effect at their respective game-relevant velocities. Also, just having a rough surface texture can be enough to cause turbulence, since it causes the air to stick more to the surface. In my experience, ping pong balls have a definite texture to them, and unless you polished that sanded-down golf ball to a mirror finish, it probably has a non-smooth texture too.