The reason for giving the "kill" to abhinandan is mentioned by the then IAF chief. I wrote that here too, but it is lost and no pakistani want to listen to it.
However - I don't think Indian govt is giving away this award without confirmation.
The only confirmation we have is that Abhinandan demonstrated great bravery and fired the missiles at Pak Fighters. The award should be limited to his bravery of fighting with an antiquated fighter called MIG-21 and not shooting down the Pak fighter.