James Kelly Nestruck said he received a contract between Wests Tigers forward Martin Taupau and the Manly Sea Eagles.
The two clubs have confirmed the transfer.
A possible explanation for the mix-up is that Mr Nestruck has the same initial and surname as the CEO of the Sea Eagles, Joe Kelly.
But in a statement the Wests Tigers denied that they had sent the email.
Mr Nestruck made light of the incident on his Twitter account, having become an unlikely trending topic in Sydney.
"Hey there Antipodean rugby enthusiasts... Thanks for all the interest, but I'm done playing at Kiwileaks now - and am off to review a play," he said.
A Canadian theatre critic has said he was accidentally sent an email revealing that a rugby league star is switching clubs in Australia.