Class extending itself?

I encountered a PHP class written by a previous employee that is defined like this:

namespace SomeNamespace;

class SomeClass extends ::SomeClass
{
    private function __construct() {}

    public static function someFunction()
    {
        //Do something
    }
}

Would somebody please explain what is going on here? Is this class extending itself? I know a singleton would use a private constructor, but not sure that is what is happening here.

The actual class has to do with caching. Not sure if that helps.