I think it may just be a default saying, but on the Alabama OC map page it says:

"NOTE: Almost all states allow local regulation of the discharge of firearms"

Alabama prohibits regulation, even the regulation of discharge, of handguns by localities:

http://www.ago.alabama.gov/pdfopinions/2005-127.pdf

Seems like localities can regulate the discharge of firearms for hunting, it's unclear if discharge can be regulated for non-hunting. But it's pretty clear that regulations cannot apply to pistols.