I spent some time going over your article. It's a nice bit of detective work, and your description is quite clear. Nevertheless, I think the photo can be explained using the currently accepted arrangement of the suite.
To understand what was going on, I drew a diagram as close to scale as I could manage given the information available. The red lines are sight lines from the camera to the mirrored cabin.
The vertical surface you identified as a door seems to line up with the foyer wall in my diagram. The edge of the window shows up about where we'd expect it as well. A door from the 1st class entrance to the foyer, such as you hypothesize, would extend further into the corridor than what we see in the photo, almost coinciding with the edge of the window. Even allowing for inaccuracies in my drawing, it's hard to see how such a door could be present.
I don't have a good explanation for the horizontal line you identified as the top of the door; it actually seems to extend beyond the door. It's too low to be a beam from the deck above. It may be the rebate of the door frame, but I wonder if it's simply a scratch on the photo.
I used estimated dimensions in several places, so this should not be considered the final word on the layout. If anyone spots any errors in my drawing I'd be glad to hear of it.