Bharat Ratna is not a title under Article 18. Clause 1 of article 18 covers exceptions like academic or military titles. Awards like Padma Vibhushan, Padma Shri etc. can be given to the citizens for exceptional and distinguished services rendered in art, literature, science and other fields.
In the case of Balaji Raghavan v. Union of India, AIR 1996, the court said that National awards aren’t titles under clause 1 of Article 18. The court asked for setting up guidelines while giving these awards as they are highly respected.