The Mirror Thing is amusing for being unintentionally self-defeating: it has already been established that future mirrors simply are like that - the mirror image can be 3D, made to rotate, linger and for all we know dance polka out of synch with the thing being mirrored.
I assumed the Mirror Thing was just for us. I mean it's not like we're going to have Stamets say "Hey Captain, my mirror is doing this weird thing." Kind of like the reflection of Benny Russell in the window in Far Beyond the Stars... it wasn't actually there, right?