It even appears that Manuscripts in the Rambam's own hand have been discovered there.
The Rambam in Yesodei HaTorah 6:8 seems to require Genizah ONLY for Sifre Torah. While the Touger edition cites SA YD 282:23 as well as the Magen Avraham 154:9 "differ and require all sacred texts to be entombed."
This Humra seems to go beyond the Rambam's requirement. However the Genizah in Cairo had many holy texts aside from Sifrei Torah. Was the Cairo community Machmir despite the Rambam? Or did the Rambam himself communicate a more strict version of this Halachah outside the precincts of his Mishneh Torah and this extra-textual version survived.
Or perhaps there was another dynamic at work here?