What effect does an unnamed namespace have on a class?

I was looking over some (C++) code and found something like this:

//Foo.cpp
namespace
{
    void SomeHelperFunctionA() {}
    void SomeHelperFunctionB() {}
    void SomeHelperFunctionC() {}

    //etc...    

    class SomeClass //<---
    {
        //Impl
    };
}

SomeHelperFunction[A-Z] are functions that are only needed in that translation unit, so I understand why they're in an unnamed namespace. Similarly, SomeClass is also only required in that translation unit, but I was under the impression that you could have classes with identical names in different translation units without any sort of naming collisions provided that you didn't have a global class declaration (e.g., in a commonly included header file).

I should also mention that this particular translation unit does not include any headers that might declare a class with an identical name (SomeClass).

So, given this information, could someone please shed some light on why the original programmer might have done this? Perhaps just as a precaution for the future?

I'll be honest, I've never seen classes used in unnamed namespaces before.