Sure doesnt sound like that to me.

A backdoor is a typically covert method of bypassing normal authentication or encryption in a computer, product, embedded device (e.g. a home router), or its embodiment

Source: https://en.wikipedia.org/wiki/Backdoor_(computing)

Not very covert if it is offered to a user.
If MS gives up the key that is stored plainly in their system, that is a problem. But not a backdoor.
This is quite literally the police knocking on the front door and demanding the key.