I have also not heard that. The only thing I can guess he means is maybe the visibility of any cuts, or the proximity to major organs/veins/arteries...? Maybe what is your dominant hand if cutting on your arms (though my scars would throw anyone off about that). Oh, and genital cutting strongly correlates with sexual abuse or assault history. But that's all I can think of.
I have not encountered anything specific in the literature besides the correlation to sexual assault though, so I think anything else he may be talking about is either inferred soley by him, or in a small circle that has not published anything either peer-reviewed or otherwise.