As per the Election Commission of India website- A service
voter may appoint any person as his/her proxy to give a vote on his/her behalf
and in his/her name at the polling station.The proxy shall have to be an ordinary resident of that constituency. He need not be a registered voter, but
he/she must not be disqualified to be registered as a voter.
So, the proxy need not be a registered voter in
the same constituency.
@Hopeless can you kindly tell which tests have different
explanations, so we can update the explanation at our end.