If Bitcoin was created by Nick alone, then we would all know about it, Nick would make sure of that.
There would be no Satoshi, the author would be Nick Szabo.
However Nick is not Satoshi, but he certainly knows who is, or was, behind the creation of Bitcoin.
If I am the one who created Bitcoin then I would make sure that it will be known to anyone who knows about cryptocurrency instead of using different name or alias and then later on will claim that I am the one who created Bitcoin. It should have been as what you have explained where the author would be Nick Szabo and not Satoshi Nakamoto. It is possible that he is doing it for a certain reason and to do it is which he will claim that he is Satoshi Nakamoto and letter S and N is based on his name (which we all know that it's only a coincidence that the initials are both S and N.
