If it was migraine with aura, then can we know a little more about the symptoms. In particular, if it was a scintillating pattern with a distinctive sawtooth series of white lines.
Vital to know if it was in both eyes and if there was a headache afterwards.
There is an odd thing that occurs in some people where they get a flash every time they blink. There is a disturbed area left behind which impairs vision slightly. THIS IS IN ONE EYE ONLY. It also often follows eating sharp/sour fruit. There is no headache. I doubt this has anything to do with migraine, but I'm not sure.
The thing about having migraine diagnosed, is that it marks one's medical records for ever. But risk missing a brain tumor? Tough call.
I'm as convinced as anyone can be that chocolate is a trigger for migraine. Say, 90% certain. The prime cause I still think is deep seated worry - anything else being a trigger.