daasyochid- NOPE ! You are misquoting the Rambam and, dare I say, misrepresenting what R’ Yaakov MAY have said. The Rambam- in the halocho that you mention- does NOT speak about the moon (or other heavenly bodies) at all. He speaks about “malochim”- angels. Please check again.
And,actually ,in the mishne before that (3), he specifically addresses the heavenly bodies and says that THEY ARE PHYSICAL- just the opposite that you said. What he says is that that world- “olam hagalgalim”- is fixed and never changes- in contrast to the living world (us) that changes all the time (birth, growth, death).
I don’t know what R’Yaakov zz’l said but ,based on this Rambam, he clearly did not say anything that is being quoted.