Regeneration takes SOOT (aka diesel combustion byproduct) and burns it off. The result is ASH (technically, stuff that can't burn off\down any more).... so think of when you have a camp fire and when it's all done, you have a pile of ash... no matter how much you try to burn that down, there's no combustible stuff left, so it never goes away... you eventually have to dig out you firepit to clean it.
Based on your reported value (check with others with similar engine code and you'll see the massive discrepancy), your system was reset, your ECU was reset, your ECU was replaced, your DPF was replaced, or a combination of those.....
There's no way at that age/milage you have such little ash.