What is the gray dust stuff that comes out of the vacuum bags/collector? ?

I was cleaning my new vacuum out, I have a dyson. I noticed that there was some gray dust like stuff at the bottom of the container? Is this dirt? or just crap that gets stuck in the carpet? I'm a clean freak so this is a shock to me.

I vacuum my house every day. I'm very picky about it being spotless all the time. And within a week, I have at least 4 inches of dust buildup in the chamber of my vacuum. I have a Hoover Empower 4600. It's just a sign that your vacuum works well!

It's a culmination of dead skin cells, dirt from outside, dust from the air that has landed on the floor, pet dander, and pollen.