Eating a large bar of dark chocolate should differentiate, purely in the interests of science of course.
Out of curiosity, does chocolate have any other effects on you besides the acne? Like easier bleeding/blood thinning? Or other inflammation besides acne? It has more than one effect on me and I surely can't be the only one observing it.
I consume chocolate in the evening and do sometimes clear walking tracks before breakfast, which often involves scratches. So I would expect to have noticed wounds bleeding for longer than usual.
Also, I would add that most processed dairy (besides just plain old milk) is mixed with many other detrimental ingredients. So there may be a cause/effect relationship overlap with other foods.