That’s not a Machlokes on Ikkarim. It is a Machlokes on numbers.
The Rambam also held of Sisrei Torah. He spoke of it often, and dedicated more than a Perek in the Yad to that. The question is only what is the Sisrei Torah. –side point
Besides, when I say that he didn’t make them up it still doesn’t have to mean it is Mefurash. They aren’t personal musings. It is what he took from the words of Chazal.