The text provided gives the impression Ajahn Chah is saying there is a "knower" outside of the "five aggregates". If this is so, this appears certainly to be a wrong view (but something common in the village jungle dharma of North East Thailand).
I think the language of Ajahn Chah is confusing when he emphasises the conventional literal meaning of 'Buddho' meaning "the one who knows". In reality, Buddho is not a person. Instead, Buddho is "the mind that knows". Therefore, Buddho is not separate from the mind. As Ajahn Chah says:
There is the "average mind" that is untrained & undeveloped; which reacts emotionally with annoyance to sounds.
There is the "refined mind" that knows in accordance with the truth; ñānadassana; "the power of the refined mind, so that it knows the sound as simply sound"; "the mind lets go".
Ajahn Chah is referring to "untrained average mind" versus "trained refined mind". There are too many suttas that say "the mind" ("citta") is enlightened, such as:
Visaṅkhāragataṃ cittaṃ, taṇhānaṃ khayamajjhagā
The mind has reached the Unconditioned; attained the destruction of craving.
Dhammapada 154
Nāhaṃ, bhikkhave, aññaṃ ekadhammampi samanupassāmi yaṃ evaṃ bhāvitaṃ bahulīkataṃ sukhādhivahaṃ hoti yathayidaṃ, bhikkhave, cittaṃ. Cittaṃ,
bhikkhave, bhāvitaṃ bahulīkataṃ sukhādhivahaṃ hotī
I don’t envision a single thing that, when developed & cultivated, brings about such happiness as the mind. The mind, when developed & cultivated, brings about happiness.
AN 1.30
Also, there are many suttas that say the Buddha is not a "person", such as SN 22.85.
Also, the phrase: "beyond the mind" is confusing. I cannot recall such a phrase existing in the Pali suttas. In the Pali suttas, the common phrase for "liberation" is "beyond the world" ("lokuttara").
While Nibbana as an element is "beyond the mind", Nibbana can only be known by the mind. Thus Nibbana is called a sense object (ayatana - Ud 8.1).
There is no "one" or "person" that is beyond the mind. As I already posted, what becomes liberated is the mind.
For example, what "knows" is the mind. To paraphrase Ajahn Chah:
This mind that knows is a step beyond the mind.It is that which knows
the state of the mind and is not attached to the state of mind.
Thus Ajahn Chah obviously would have wrong view if he actually said "the one that knows" is not the mind, as follows:
The mind is the mind. That which knows the mind as simply mind is the one who knows.
if Ajahn Chah believed in a self or a knower outside of the five aggregates, this would be a wrong view. The Buddha never taught about a "knower" outside of the five aggregates. For example, the Buddha taught:
“Wisdom and consciousness— “Yā cāvuso, paññā yañca viññāṇaṃ—
these things are mixed, not separate. ime dhammā saṃsaṭṭhā, no
visaṃsaṭṭhā.
And you can never completely dissect them so as to describe the
difference between them. Na ca labbhā imesaṃ dhammānaṃ vinibbhujitvā
vinibbhujitvā nānākaraṇaṃ paññāpetuṃ.
For you understand what you cognize, and you cognize what you
understand. Yaṃ hāvuso, pajānāti taṃ vijānāti, yaṃ vijānāti taṃ
pajānāti.
That’s why these things are mixed, not separate. Tasmā ime dhammā
saṃsaṭṭhā, no visaṃsaṭṭhā.
And you can never completely dissect them so as to describe the
difference between them. Na ca labbhā imesaṃ dhammānaṃ vinibbhujitvā
vinibbhujitvā nānākaraṇaṃ paññāpetun”ti.
Wisdom & consciousness are inseparable. If the Buddha was to be defined in terms of aggregates (even though the suttas discourage this), the Buddha would be defined as "wisdom consciousness" or "wisdom mind/citta" or "Dhamma/Truth-knower", as follows:
I am now old, aged, burdened with years, advanced in life, and come to
the last stage: my years have turned eighty... Sariputta, even if you
have to carry me about on a bed, still there will be no change in the
lucidity of the Tathagata's wisdom.
MN 12
Otherwise the Buddha is more accurately defined as the embodiment of Dhamma itself, i.e., the Buddha is defined as "not-self" ("anatta") & "emptiness" ("sunnata"), as follows:
Enough, Vakkali! What is there to see in this vile body? He who sees
Dhamma, Vakkali, sees me; he who sees me sees Dhamma. Truly seeing
Dhamma, one sees me; seeing me one sees Dhamma.
Vakkali Sutta
However, in conclusion, the Buddha is not a "One" or "Self" or "Knower" outside of the five aggregates. There can be no "knower" outside of the mind. What knows is the mind.