There is a difference. OIC is not a "Muslim lovers" group - It was formed to (quoting wiki)
"Muslim governments would consult with a view to promoting among themselves close cooperation and mutual assistance in the economic, scientific, cultural and spiritual fields, inspired by the immortal teachings of Islam."
WIth the world's 2nd largest muslim population, India would be right to be interested in participating in OIC. Economic, Scientific, Cultural and Spiritual - which if these do not apply to Indian muslims?
Secondly the OIC member states will benefit tremendously learning from India (not saying this egotistically) aspects of development, diversity management and diplomacy
From India's pov, while they already have close soperations with almost all muslim countries of substance, OIC membership will help rectify some very wrong perceptions some ill-informed muslims have
BUT and it is big BUT ! - I am not sure if India will actually seek OIC membership. Congress coalition may see it as a minor addition to their weak election arsenal