I don't think this is what Keen claims, or the designer of that model for that matter. They're talking about credit extension on the basis of monetary expansion. It really is a form of base money creation that happens independently from the control of the central bank.
When you look at the phenomenon of vendor financing, it is actually not a very strange thing at all that such a thing can happen. For the a government to render it "illegal" for example would disrupt one of the most elementary functions of a market economy. Let me explain:
Take a situation in which a producer of a good has $100 in possession and wants to sell a good to a client on the basis of a loan. For this purpose it can make use of two separate basic economic transactions: first lending the $100 to the client and then accepting the money back as payment for the produced good. The result is that the money goes from producer to client, back to the producer. The good goes from the producer to the client and an IOU for the future payment of $100 is issued by the client and given to the producer.
Now let's make one simple shortcut: instead of making the money change hands twice only to end up in the same place at the end of the transaction, we simply make it not change hands at all. The good is simply exchanged for the newly issued IOU.
Now let's observe an interesting implication: this second process can take place even when there is no money in possession by either person in the first place. When this happens, the situation is equivalent to one in which money is temporarily created ex nihilo to settle the transaction. This is to say, if we were to disallow the exchange of a good for an IOU, the process would be impossible to perform without the creation of new money out of nothing. This is why money creation in the process of extending credit is a very normal thing.