Answer:
It is only a norm that only a Sinhalese Buddhist can become a president in Sri Lanka. According to the Article 31 of the Sri Lankan constitution it says any citizen can become a president!
The election and the term of office of President.
31. (1) Any citizen who is qualified to be elected to the office of President may be nominated as a candidate for such office -
(a) by a recognized political party, or
(b) if he is or has been an elected member of the legislature, by any other political party or by an elector whose name has been entered in any register of electors.