Unless you can withdraw funds to another wallet address (non custodial), it is probably a scam.
Please provide more details so that I can better understand your offer.
I am sure he going to ask you to register for an account on a platform and send you the BTC, thinking you'd send on-chain ETH to his/her wallet address.
It's better to avoid a transaction like this with OP judging by the post history the account.
It should be on a wallet-to-wallet basis, not sending his BTC from a questionable exchange and then you will send Ethereum on the chain, that's ridiculous, you are an idiot to fall into this scheme based on his post history this guy is trying to scam people who will fall to this trap not knowing that we know this kind of scheme, imagine asking for a loan in exchange for collateral that's in a questionable and new exchange.
We should tag this account so people will know his scheme.