Well the site explains how to go from duality to non-duality based upon observations.
Page 7 until page 11 are all about explaining reality and the universe.
No physical universe? The universe is nothing? It seems to me that you totally lost connection with reality.
Try holding one hand horizontally and holding a lighter in your other hand a few centimers below the hand you are holding horizontally. Now lit the lighter and see how long you can maintain your view that the universe is nothing and that it is just a concept.
You will become conscious of a burning feeling, because you experience this, it is real. You get this burning feeling because the temperature from the fire out of the lighter hits the nerve cells in your hand. The nerve cells in your hand send a signal, via neurotransmitters, to your brain where you become conscious of a feeling. The lighter however is not created by your consciousness, you become conscious of the lighter when you see and feel it. The lighter however is constructed in a factory. The concept of the lighter, as in the word 'lighter', is a construct of consciousness, constructed by your intellect sense, thought thought, in the mind.
As consciousness is awareness, what would you be aware or conscious of, if you had no eyes, ears, nose, mouth, nerves or brain?
They are mutually dependent, this means they are identical or you can not separate them. Consciousness exists in reality; the body, from which consciousness arises, exists in reality. Therefore; consciousness depends on reality. However that what you perceive/ are conscious of/ are aware of, is reality; so reality is also dependent upon consciousness. If you had read the whole text you would have read this. However, it is not that easy to comprehend.
Again, it seems you have not read the whole text. If you had, you would have read that page 1 until 6 are about seeing through the mental construct of the self, page 7 until 11 are about the nature of reality, page 12 is about what it all means, and page 13 is about how to deal with the insights and knowledge in every day life.
There is only non-duality or duality. As enlightenment is just a feeling, this feeling can be weak or strong.
Based upon your reaction I presume you did not read the whole text, but just some pages or part of a page. As stated on the front page of the website, it reads as a book and the pages have a logical order. If you jump in half way, it is almost the same as if you were dropped somewhere in a very big forest and have to find the path. So may I advice you to read the whole thing? It only takes you up to 2 hours probably.