std::thread constructor pass by reference when using a class member function

I've done quite a bit of research on the new c++11 rvalue and carried over lvalue. Here is a sample of what I have found and read:

what-does-t-double-ampersand-mean-in-c11

how-stdthread-constructor-detects-rvalue-reference

stdthread-and-rvalue-reference

I have also briefed myself on rvalue references

Move_Semantics

rvalue_references

A Proposal to Add an Rvalue Reference to the C++ Language

Specifically, regarding the std::thread constructor, I found

how-to-create-a-thread-inside-a-class-function

and used one of the answers to write some simple code

#pragma once
#ifndef CONSUMER_H
#define CONSUMER_H

#include "Mailbox.h"
#include <thread>
#include <iostream>

class Consumer
{
private:
    Mailbox mailbox;
    std::thread consumer;
public:
    Consumer(Mailbox& newMailbox);
    ~Consumer();
    void operator()() { std::cout << consumer.get_id() << "starting\n"; }
    void start();
    void run();
};

Consumer::Consumer(Mailbox& newMailbox)
{
    this->mailbox = newMailbox;
}

void Consumer::start()
{
    consumer = std::thread(&Consumer::run, this); <-- need understanding
}

#endif

Checking the `std::thread constructor

std::thread::Thread

I observe a template that uses rvalue parameters. I understand that a std::thread can be initiated through a simple example

void run(void) {std::cout << "I'm running";}

std::thread(run);

which appears straight-forward until I am inside a class whereby I need to do the following

consumer = std::thread(&Consumer::run, this); <-- need understanding

because I learned from Jonathan Wakely that run() is a non-static member function and has to be run on an object. How is the new thread supposed to know which object to call it on if you don't tell it?

This makes some sense but the need to pass by reference the class function doesn't since I have seen A a; A&& ref = A() possible. I'm super confused about rvalues and just want to understand why the code I wrote above is necessary to pass the function to std::thread.

I feel certain I also don't understand variadic templates that well either which compounds my understand of the std::thread variadic template constructor.