There is no reason why he should be taken as an authority.
"anything transient is false" is wrong at so many levels.
So anything transient cannot be the self, hence is an illusion, or false.
But yes i also believe it's quite wrong ^^
Buddhism can deny self, but Buddha can also say, his self alone exists.
In any case, these are just beliefs. We know the world exists and there are no souls around. So much for "enlightenment".
solipsism
Enlightenment is profound, and unrelated to belief, or non-belief about the existence of the world. Mainstream Buddhism does not deny the existence of the world or individual persons, it states that our conception of the "self" is a mental construct.
From a subjective perspective, everything we experience is mind-constructed, and in that context, there is no difference between self and world; everything we experience is mind. This is the essence of buddhist non-duality.
I would further add that we do not know anything about the existence of the world, only that we perceive the world indirectly based on sensory input, and most of us conclude that the world actually exists. There is a movement in science that calls this fundamental belief into question, you can checkout writings and interviews with Donald Hoffman.
"Hoffman notes that the commonly held view that brain activity causes conscious experience has, so far, proved to be intractable in terms of scientific explanation"
That's just a fringe position. It may look good on Youtube or a TED Talk. But it has no scientific backing. It is certainly not a "movement" in science. They produced no evidence or even proposed any experiments. It's just idle speculation, not science.
A bit pedantic, and I could be wrong, but based on what I've read, my understanding is that Advaita (non-dualism) is not something you can practice, although there are practices in that school that can advance you on the path, like shravana, manana, nidhidyaasana.
It's more of a reasoning-, knowledge- and understanding-based system than anything else.
Jnana Yoga is the path.
Check out Swami Sarvapriyananda's talks on YouTube about Advaita.