Article 13 of the Indian Constitution provides for the protection of Fundamental Rights and declares that any law inconsistent with or in derogation of Part III of the Constitution shall be void to the extent of the inconsistency.

To prevent the State from bypassing Fundamental Rights through executive or traditional means, Article 13(3)(a) provides a highly expansive definition of the term "law". It explicitly states that "law" includes any Ordinance, order, bye-law, rule, regulation, notification, custom or usage having in the territory of India the force of law.

Therefore, the view of 'Y' that the term 'law' includes custom or usage is absolutely correct. Because "custom or usage" is expressly listed in the constitutional text, uncodified traditional practices that hold the force of law are subject to the exact same constitutional scrutiny as formal legislative statutes.

'X' is incorrect in doubting or rejecting the inclusion of custom or usage within the definition of law under Article 13. Thus, regarding the point of contention, only the view of 'Y' is correct.

Therefore, the correct option is D.