Well if you read the article...

  “It is very easy to get Bluetooth fitted in the ears. It is attached to the ear temporarily and can be removed. Such a technique was used by a Vyapam scam accused too to clear his medical exam eight years ago.”

And the article also mentions that the Indian Supreme Court themselves cancelled the licenses for 634 doctors licenses issued between 2008 - 2013.. some of which used this same technique.

How it works, where does it go; I have no idea. But clearly it's not a one-off case.

P.S. I think that it's perhaps surgically clipped deep in the inner ear somehow, and not inserted beneath the skin.