So in Hua-yan teaching, there are two levels of existence (two dharma realms): the multiplicity of phenomena and the One Mind.
The One Mind is also known as “the True Thusness” or “substance” (or noumenon; ultimate reality).
In this sense, the One Mind is like the mirror, and the phenomena of the world are like the reflections in that mirror.
Thus, different people come in front of the one, same mirror, but each person looks different in front of the same mirror.