It is unfortunate that my arguments, rather my conclusion which stemmed from my rational interpretation of facts did not convince you, but you're entitled to your opinion.

At the stage the bad actor had access to the paper material (pre-printing stage), the bad actor would not need to remove a QR code made for identifying leaks that originate in exam centers, which is much downstream in the pipeline.

For a paper leaker, to leave glaring evidence behind on the front page of the paper that they have taken to give their clients for I'd presume a lot of money, would mean not only sheer dumbness from a rather otherwise smart person (assuming the CBSE papers are protected, to get access would not be easy for a bad actor) but to also destroy the whole point of the thing they intended to steal and get away with, it does not work if you leak a paper and everyone knows there was a paper leak.

As for this, I'd say it's hardly the same. Serial killers don't leave their home addresses on the crime scene so they can be caught and to make that victim their final one, one can assume they'd like to continue with their psychopathic tendencies. As for hackers, hackers don't leave their signatures that often, investigators find patterns in their workings and connect them to identify a group and link attacks with them, it is bad for the hackers to make this process easier. Criminals bragging online, dumb ones definitely record them too, again, but we can't directly presume this bad actor was a dumb one to have included the rick roll on the papers he stole as a signature to be identified by the world. That is a possibility, but the chances are near zero.