I don't think so. That's a phonological rule that states that ん becomes assimilated to the place of articulation of the consonant that follows it. So it becomes "m" before "b" and "p," "n" before "t" and "d" (and I believe "s" and "z" too, but I'll have to check to be absolutely certain about that one), "ng" before "k" and "g," etc. The old む was a conjugation of the verb, just like (よ)う is nowadays.