this guy has never been practicing muslim,
so they have nothing to cry about.
I think it is more that his position towards israel
gets him in trouble with extremists.
He is considered a Muslim by other Muslims regardless of how well or poorly he practiced it, and now is considered an apostate because he specifically rejected it.
His attitude towards Israel was obviously not popular with them, but at the same time, they probably ignored it as simply the ravings of an intellectual. But I think his conversion is going to be interpreted by them as a much more direct challenge.
So far, the response has been muted. He’s Egyptian by birth, and the Egyptian imams have not called for his head, so that’s a good sign!