The meanings are

A. not any member of our group (i.e. no person among those in our group)


> We are, **none of us**, perfect.  
>
> We are, **not one of us**, perfect.
>
> There is, **none of us**, but has some flaw in his character. 
>
> There is, **not one of us**, but has some flaw in his character.


B.  not a member of our group (i.e. does not belong to our group)


> He is from another (country, tribe, group, clan, county, ... whatever). He's **not one of us**.

In the 18th c. and earlier, "none of us" could be used to mean "not one of us", not a member of our group, and the usage has survived in regional dialects.


> A stranger, he is. He's none of us.