This absolutely is not the case, as any collateralize loans require you to transfer custody to a 3rd party making the loan.

Otherwise, you could just steal the coins straight after handing over the private keys. And even if that wasn't the case, the loaner will want exclusive control and move them to another key they control anyway.

If it was a loan, you would have blockchain records of movement of Satoshi coins. This can be proven not to be the case, and so we can be quite confident there was no loans to Satoshi.

Not sure I understand. Why couldn't you just escrow the private key with a mutually trusted third party, and back the whole thing with a contract. You know - with a traditional bank, that has a contract with you, knows your identity, and can report you to the authorities - and sue you - if you default or sell the collateral you've provided for the loan?