Hard to tell... Others have mentioned typical reasons for visa applications to be referred back to New Delhi for additional checks - any sort of connections with Pakistan, disclosure of anything remotely connected to journalism, religious / missionary work, etc. Note, even volunteering seemingly innocuous information like "photography" as an interest or planned activity in India as a tourist can have your application flagged as a potential journalist. Also, do any of your parents/grandparents have any connection to (British) India, as in they were born in India or Pakistan, etc.? Any of these things can trigger additional checks. If you have any family connection to India, sometimes they do reject the application after review to tell you to re-apply for a different type of visa (X or Entry visa).