From the paper, it seems like that the blood flow changes and the seizures are both caused by the increased processing load in the visual cortex; with the seizures also resulting from some faulty wiring in localizing that increased load to only the visual cortex. So, more like A->B and A->C instead of A->B->C. But I'd bet this visual stimuli is even more effective at causing seizures in vulnerable people than an unfortunate pokemon episode.