Read the 3rd sentence in that article....
"The ordinance increases the age required to purchase a gun in the city to 21 years old, bans "assault rifles" within city limits and mandates a license to carry."
On the new ATF 4473 forms you now have to answer a question as to: Do you "Reside in the city limits?" Yes, No or unknown is what you have to check off in one of the boxes.
Call me silly but I see a pattern here.
If a city passes an ordnance banning stuff in the city limits and you do live in the city limits of that given jurisdiction you could be lying on the form / breaking the law.
Just my .02.