From my understanding from that statement, get fan grill and remove mesh grill to improve airflow. OR use the mesh to reduce dust, but result in lower airflow

It doesn't. That statement was better airflow when compared to mesh.
The grille is just supposed to protect the fan from being hit/touched and damaged by something AFAIK

to ensure that the airflow is not too restricted. << this implies grille also restrict airflow, but not as much as mesh