Why do private member variables behaved like protected in the same module when creating deriving class?

[12345swordy]

On Friday, 26 October 2018 at 18:40:36 UTC, Adam D. Ruppe wrote:
> On Friday, 26 October 2018 at 18:16:38 UTC, 12345swordy wrote:
>> Why private member variables behave like protected member 
>> variables in the same module?
>
> I don't understand, what do you mean?

I am referring to the class private member variable.