Extremist is definitely too harsh of a word. Perhaps we should try passionately religious. Lots of Amish people live in the rural areas surrounding my hometown of Ft. Wayne, IN. Many of their school age children attended the public schools that were offered in their area. The Amish definitely have very strong beliefs. Should the school change it's curiculum for them? Personally, I think not.
The Muslims in question are most likely much more similar to the Amish than to the terrorists, but that still doesn't mean that the art class should be entirely reworked just for them.