Non Viable Particle Count

Why in revised guidelines . For ISO Class 5 , stop consideration of 5 micron partical count. If any count comes. What’s it meaning.

https://www.pharmout.net/iso-14644-1-2015-update-cleanroom-classification/

5 micron particle having greater size easily settle down with time.The increasing count results in risk of sterility of product b/c particle is carrier of bacteria and fungi.