This is crazy. How can a tweet cause a seizure?
I don’t believe it at all.
A light strobes at a certain frequency (2/second?) can cause seizures even in people without a history of seizures.
There was an animated Japanese series some years ago that was causing kids watching it to have seizures.
The tweet had an animated GIF file that strobed pasted into it. It launched as soon as he read it. There was no way for him to avoid it.