If this is a fed mandated backdoor, I guarantee Microsoft/Windows isn't the only one either, they are just the only/first ones to get caught. I'd be suspicious about every single commercial, closed source operating system or encryption product in the US right now.
It also doesn't help this comes from a person who likely was close to the development at Microsoft (one way or another) as their recent disclosures are quite alarming.
Of course, this could technically be the stars aligning type bug, but it seems like a purposefully planted backdoor to me.
Which leaves an enormous attack surface. If you can break Windows before logging in, you can effectively bypass bitlocker.
"Windows loads some file in System Volume Information automatically" is not evidence of a backdoor. And you have to put specific exploit files in there to turn this into an attack. You don't just make the folder.
It's still possible this is a backdoor, I guess, but there's nothing as blatant as you're implying.