Indonesian pictures could have been taken when she was visiting a place of religious significance?
Yup, she only used it during her visit to Istiqlal Mosque (Indonesia's largest mosque).
This picture for example was taken from the same presidential trip to Indonesia.
its not the official religion, its one of the 5 recognised religion along with Christian, Protestant, Budha and Hindu
also due to the above, people that don't practice one of the five religion will just put Islam on their ID card which inflate the % of Muslim here
True, i don't even consider myself a muslim but had to put islam as my religion due to administrational matter.