If he was reciting the Koran and was registered at the school as a Muslim, that's all he needed to do to BE a Muslim, under Islamic law.
Did you read about the Coptic Christian lady who is being prosecuted in Egypt, because her estranged father briefly converted to Islam? The government is requiring that she BE Islamic, or be deemed an apostate.
It opens up a serious can of worms.
Muslims are not allowed to join Christian churches. If he is a clandestine Muslim, I would think he would be spending time with some Muslims.
Only Hillary is doing that.