Are all the "scratches" on the surface is something Blender generated, or you painted somewhere ?

Hi,

During 5:00 - 5:30 in the video, we dealt with multiRes Ambient Occulsion bake. Suddenly we get all these "scratches" on the surface. My question is - Are all the "scratches" on the surface something Blender generated from the baking process , or you pre designed the surface - or painted somewhere and coupled with the Bake - this was the end result ?

And if the baking process alone causes this effect - How does it know where to put the "wear and tear" on the object ? is it according to the Creveces and edges ? 

If it's not only the effect but you actually had to apply a pre made map  - where is that stage executed ?

I'm a little baffled.. It just looks too good :)

Thanks and all the best,

Ido