Since we are citing the Constitutions definition, it is of fundamental relevance to state that Sikhs did not accept the Constitution itself. The reason they did not accept it is because minority rights were not protected (because the Constitution did not even recognize the minorities to be separate from Hindus.)

 "On 27th August 1947, the Constituent Assembly of India had passed a resolution that the question of minority rights in Eastern Punjab will be considered separately but subsequently minorities subcommittee recommended that no special safeguards will be provided to the Sikhs... Sikh representative Sardar Hukam Singh and Bhupinder Singh Mann had refused to append their signatures to the Constitution of India and Sardar Hukam Singh on 21st November, 1949 declared in the Constituent Assembly  “Let it not be misunderstood that the Sikh community has agreed to this Constitution. I wish to record an emphatic protest here. My community cannot subscribe its assent to this historic document.”"

"no special safeguards will be provided to the Sikhs" is equal in part to Sikhs not being regarded as a distinct minority. In the following 65 years, this issue has come up many times, and Sikhs have always objected to the Constitutional definition, and for not having agreed to it.