notary public affidavit for oci card

I don't understand why they want notary affidavit for OCI card.
my son born India got British passport in India, father British OCI card holder, mother Indian,
1) do we have to renunciation his Indian nationality as never applied from birth Indian nationality. High commission of Indian asked notary public affidavit our son never have Indian passport.
2) do we have to apply in vfs office London his surrender certificate as he never ever have Indian passport from birth.
I don't understand what to do. Please help