So, given the lender is asking for collateral (to cover losses by borrowers defaulting) and is prepared to use an escrow, what is the scam?
I could not tell them as a scammer and their activity could not be a scam activity. But the person has mentioned that s/he has sent the bitcoin to the borrower's wallet which s/he has not done. That means s/he was trying to scam by showing that s/he is providing a loan and s/he is a legit user which s/he is not.