Modem-routers often have subtly different models (sometimes even under the same model number and SKU!) in different regions. "Subtly different" can mean in this instance: completely different OS, different chipset/hardware/board supplier etc.
It's possible that the models affected by this particular attack aren't sold in other places, or perhaps they are, but are actually still different (enough). Or they are just not widely used.
I say this because govt. organisations have often issued warnings and recommendations like this in similar circumstances, e.g. a while ago some modem-routers widely used in this country were attacked, and a warning very much like this has been issued.
It's possible that the models affected by this particular attack aren't sold in other places, or perhaps they are, but are actually still different (enough). Or they are just not widely used.
I say this because govt. organisations have often issued warnings and recommendations like this in similar circumstances, e.g. a while ago some modem-routers widely used in this country were attacked, and a warning very much like this has been issued.