I hope there is more to this story.
As someone who lives with Epilepsy and a seizure disorder there would not be a cruise site, message board or news outlet that would not know about this situation if it happened to me.
I have to say that I have had seizures on the ship with no problem except for a Princess doctor who administered a ridiculously low dose of medication when, one time, I did not have mine with me. My wife returned to our cabin and retrieved the correct dosage and all was fine.
If the disorder is medically managed there is absolutely no reason to have put them off because of one seizure. Especially if the cause of the seizure (failure to take daily medication) was known. However, I do find it strange that someone with the disorder would forget their meds.
Epilepsy and those who live with have suffered an undeserving stigma for many years and I hope that it was not just a narrow minded Captain that was the reason for being put off the ship.