There are many visual metaphors in Zen which appear to be about reflection: the moon in water, the moon in a dewdrop, and the mirror. The crucial thing is not to see them dualistically: there isn’t a moon up in the sky; there isn’t a true person whose reflection in the mirror is false.
If we can see in this way, then we can see how the images are illuminating emptiness: it isn’t that a particular feature within the reflection is an illusion. Rather, it’s an illusion to regard that feature as being separate.
It is also helpful to see these metaphors as having a dual function: they both explain and describe zazen.
Sometimes we are like a mountain. Sometimes we are hanging in space. Sometimes we are a small bird, thrown upwards into the bright air.