Yes, true. My iot things talk with my own OpenHAB installation and therefore I do not have that issue. But a generic out of the box behaviour on most of the iot stuff is to phone home as it simply cannot be connected by an app in your phone without forwarding ports etc (which is beyond a normal user's abilities).
TFA is a a question by a person who has no idea how ip networks and client/server/app communication works.
My only point was that we do not need a special IOT isolating appliance, this can all be done with standard firewalls built in most wifi or broadband routers.