I am pretty sure I am breathing through both right now (trying on purpose to do so). I can definitely feel the breath on my tongue and hold something to my nose and smell it.

Whether air from both places actually goes into my lungs? That, I don't know. So you may be right in that regard? I really don't know. :)

Are you sure about that? I don't think that's true, not for everyone at least.

I can breathe through the nose, the mouth, and also through both at the same time.

"both at the same time" blew my mind!

For me this is the norm. I can breathe through my nose, or my nose+mouth at the same time. There is no "just breathing through mouth"