Am I right in thinking the officer had no legal right to ask for your credentials? Yes you were in your car, but he still needs RS to detain you, right?
No, you are off a little. Anyone can ask you for anything anytime they choose. Whether an officer of the law can demand something of you is a different story however. Sometimes theycan and sometimes they can't; it is up to you to know the difference if and when the time comes.
In this case, there was no legal authority to demand the document and accordingly, Kryptonian stated the officer "asked" to see it.
And now I shall continue and share my personal reality on this situation...
I give praise to Kryptonian for honoring the request in this situation by the sounds of it all. After all, there is an organization that has been going around teaching multitudes of people about their right to OC. Seing as the officer was doing nothing (having just wrapped with another task) he thought he might just make sure the citizen was aware of this particular aspect of the law also.
Now, before you (yea you, the one who's blood pressure is now on the rise, whoever you are!) light me up, let's say this...
One possible suggestion for this situation would be to respond to the officers question with something like "Of course I have a CPL, MOC made it perfectly clear that it was necessary to transport. They also made it clear that without suspicion of a crime I am not obligated to show any papers. You are aware of that too right?" Proceed from there as the situation calls for.