I've been asked a few times about whether I think the Maimonides was a Kabbalist.
My understanding is that while I don't think he was a member of the secret societies which taught Kabbalah in those days, still he was at least in the category referred to in Ethics of the Fathers as, "And they reveal to him the mysteries of the Torah."
This means by virtue of his intense devotion to Torah, he was likely granted an independent revelation of many of the mysteries which select few among the spiritually elite were being taught in secrecy via the mystical tradition.
This also explains why when he expounded on the mysteries it did not come out in the language of Kabbalah, like Sefirot or Ein Sof, but rather in his own familiar intellectual parlance; namely, the language of philosophy.