This section is summed up with the Buddha saying:
[T]here are two forms of teaching the truth attained by the Tathagatas, Arhats, Fully-Enlightened Ones of the past, present, and future. They are: the teaching by discourses, and the teaching by the establishment of self-realisation. What is meant by the studying of the discourses is this, Mahamati: there are various materials and canonical texts and discourses by which sentient beings are taught according to their dispositions and inclinations. What then is the truth of self-realisation by which the Yogins turn away from discriminating what is seen of the Mind itself? There is an exalted state of inner attainment which does not fall into the dualism of oneness and otherness, of bothness and not-bothness; which goes beyond the Citta [virtually synonymous with vijñāna (consciousness) and manas (intellect) ], Manas [intellect], and Manovijnana [mind, thought; discerning, recognizing, knowledge]; which has nothing to do with logic, reasoning, theorising, and illustrating; which has never been tasted by any bad logicians, by the philosophers, Sravakas, and Pratyekabuddhas, who have fallen into the dualistic views of being and non-being— this I call self-realisation.
So in case you were wondering, this Zen idea of a transmission outside the scriptures is, uh, captured in the scriptures, and at least since the existence of the Lankavatara, has been consistent with the Mahayana Buddhist canon.
I'd also note that this teaching of the truth isn't the whole ball of wax of Buddhism; there's actually putting these teachings into practice. Very important wording here.