Are either of you medical professionals? Probably not. OCD can very well be characterized as a disease - as it presents with signs and symptoms, and it is correlated with an actual physiological change. People with OCD typically have an atrophied frontal cortex and hippocampus.
Disorders are a type of disease, but the word disorder is much less stigmatized, hence it's use in mental "disorders". Major Depressive Disorder (MDD), for instance, is a disease - there is a change, typically again in the frontal cortex and hippocampus, as well as a change in cytokines, chemokines, and other neural and hormonal chemicals found in the body.
Further, no one here should be diagnosing someone over the internet. Using "OCD" as an insult is not only childish, it's demeaning to individuals who actually have the disease and have to live with it.
EDIT: That said, obsessing over something like this, just as some do with letter grades, is often egosyntonic and can be characterized as OCPD (Obsessive Compulsive Personality Disorder), which generally doesn't impede a patients quality of life and is very, very common.
Actually I am. I have taught psychopathology to college students for 25 years and chaired the Psychology department at my college for 15 years.
Your knowledge of OCD is sorely lacking. The OP's concerns are typical of OCDers and I suspect this is exactly what is producing his obsessive concern with light leakage.