The star has gained a cult following thanks to his unique Gangnam Style dance moves, and the track has topped charts around the world since its release in July (12).
Braun got in touch with the rapper over the summer (12) about a potential deal to manage his career, but Psy was in disbelief when he received the message.
Speaking at England's prestigious Oxford University on Wednesday (07Nov12), he says, "I receive (sic) phone call from Justin Bieber's manager, Scooter Braun. I told him, 'If you're Justin Bieber's manager, I'm Justin Bieber'. I made him email me pictures to prove who he was. I had to apologise."
Psy also admits he finally realised Gangnam Style had gone global when he saw the diverse nationalities of fans commenting on his video on YouTube.com.
He adds, "Suddenly I thought what is going on? There were English comments, and Asian people were fighting over my nationality. Is he Chinese? Is he Korean? Is he Japanese? Then Bbc, CNN are making report (sic) of me."