Mentally retarded adult and children of disbelievers may be among people of a'raaf but those didn't get the msg of Islam will be considered as believers is questionable.
Do you see any evidence in Quran and sunnah explicitly clarified this issue..?
To be honost, no I do not.
I do not have evidence for this claim, but I think this is just logic, and Islam is all about logic.
It is hard to imagine that such people still exist.
I have family living in a small village in West Turkey. until 15 years ago, no one had a pc over there. they used to trade with each other fruits and vegetables. for meat, they would hunt. they only needed money to pay for clothes, electricity and fuel for tractors etc.
only some of them had a TV. the nearest small city was a one hour drive. They did not have much contact with the rest of the world.
imagine you are born in such a village. you have a daily duty to take care of the crops on your land. your fruit and vegetables, you can trade for something else, or you can sell on a local market. you do not have internet, only a tv and newspapers.
there is no libary. you happened to live in a non-muslim community. how much chance do you have to learn about Islam? the only thing you see on TV about Islam is when there is a terroris act somewhere on the news. would you then consider Islam as the true religion? would you consider to investigate what is Islam truely about?
what you can do, is to question yourself whether the religion in your village makes sense to you or not...and if not, you can disbelieve...but to look for an alternative? where would you start? your religious leader would not advise you towards other religions...instead, he would lie or try to convince of his own religion. So you know something is not right but what?
and then you die...then what? Hell?
I think the situation of those people is not much different than of the situation of children and mentally challenged people.
If such villages existed in west turkey 15 years ago...then we can assume the world is still full with such locations where people do not have the opportunity to a little investigation about religion.
In Africa there still are a lot of people who do not have shelter, food or water...forget about tv's, newspapers, internet, etc.
even then, a lot of them are illiterate...how on Earth would they start their investigation?
the ability of reading and writing is very natural for us...but not everyone has this ability developed. these people are fully dependant on their superiors or religious leaders if they even have any.
what options do they have in life other than questioning their own religion? they can only feel that there is something wrong with it...but not much more.
Thank goodness most of those African countries are already Muslim because of the Ottoman empire...but still, there are still locations where Islam is not present.