Who would believe this lie? you have a lot of coins hiding in your balance and you don't even know what exchange to use? that's kind of BS. How come that you've took your time collecting or investing with those coins if you don't even know what exchange to sell it.
I wouldn't believe on this lie.
Either the wallet has been compromised by him or he his just making the story up and only want to gain people's attention by all means, i believe the wallet address is not his own