Nonsense. You can simply state that can simply agree to pay back an amount of bitcoin equivalent to a certain amount of gold, the most stable commodity there is. Or dollars. Or bread sticks. Or anything else you prefer.
What you are describing is a currency peg. This is what the Silk Road does with the black market items people buy on there with bitcoins. This is an acknowledgement by the Silk Road of bitcoins being a great medium of exchange due to the difficulty of tracing them, but a horrible holder of value due to their volatility.
But then you aren't really borrowing/loaning bitcoins. The transaction is taking place in whatever currency you're agreeing to pay it back as. Say currently 10bitcoins = 1oz gold. So I agree to loan you 10bitcoins, and you agree to pay me back their equivalent price of 1oz of gold +interest in 5 years in bitcoins. The loan is being taken out based on gold, and bitcoins are just an intermediary, but they are essentially acting as a certificate for that gold.
i'm not sure what his definition of a "real" currency is, but to me, a "real" currency is one in which all transactions occur within that currency. if you use bitcoin, but somewhere along the lines of a transaction you exchange mediums, it's no longer "real", you're just bartering.