The word "dinker" essentially means nothing. It's only used to because "normal unless proven otherwise" doesn't sound as exciting. What you've got there is a normal unless proven otherwise ball python, which are incredibly variable and incredibly common.
I bred a normal that looked just like that to a spider and got two spiders with a complete stripe down the back. I'm doing it again this year because my dinker normal looks as if she could be a Specter. Breeding to a morph seems to be the only way to prove things.