The doorway/wall thickness is a perspective issue, you can see it looks much thicker in the reflection off of the shower door, and there may or may not be a door visible, I can’t tell.

As for the rest, I’m not following. If the doorway is a mirror, why don’t you see any of the bathroom in it? If anything, the reflection off of the shower door make it more likely that the doorway is actually a door way. Or am I misunderstanding what you think is a mirror?