Of course, it doesn't mean the lights caused the epilepsy. These photosensitive people would have had seizures at some point anyway, but the flashing lights brought them on at that moment. One of the reasons for testing the patient is that some medications used to treat generalized epilepsy may not be as effective for treating photosensitive epilepsy. We do not yet know whether these anticonvulsants are as effective as valproic acid. If they know they have photosensitive epilepsy, yes.
People can experiment with video games and find out for themselves.
If an activity does not cause a seizure, I do not see a reason to avoid it. People need to pace themselves. Many individuals are bothered by strobe lights whether they are prone to epilepsy or not. People just need to learn how to pace themselves and know their limit when it comes to strobe light exposure. With the cartoon, my guess is that it was just a pattern in that particular episode which set off seizures.