Nice quote and one I agree with, but then I'm a Theravada practitioner.
I wonder what the "classical" Vajrayana perspective is with regards to other religions.
I was looking for quotes from major Mahayana Sutras on Buddhism on other religions, so I shall correlate the Nikaya tradition with the Mahayana claims in that these are not at all contradictory:
Here ultimately, all religions pay homage to the Tathagatha -- they are just too ignorant to know it
"I come into the hearing range of the ignorant in this Sahaloka [world of endurance - our world] in hundreds of thousands of three asamkhyeyas [numberless amounts] of names, and they talk to me under these names, yet they fail to recognise that they are all my own appellations. There are some who call me the Self-existing One (svayambhuva), the Leader (nayaka), the Remover-of-obstacles (vinayaka), the Guiding One (parinayaka), Buddha, Rishi, Bull-king, Brahma, Vishnu, Isvara [God], the Originator (pradhana), Kapila, the Destroyer (bhutanta) [or: the Extreme of Reality], the Imperishable (arishta), Nemina, Soma (moon), Fire, Rama, Vyasa, Suka, Indra, the Strong One (Balin), or Varuna; there are others who know me as Immortality (anirodhanutpada) [literally: non-Cessation, non-Arising], Emptiness, Suchness, Truth (satyata), Reality (bhutata), Limit of Reality (bhutakoti), Dharmadhatu [Realm of Dharma], Nirvana, Eternity (nitya), Sameness (samata), Non-Duality (advaya), the Imperishable (anirodha) [literally: Non-Cessation; Non-Extinction, Non-Ending], Formless (animitta) [literally: Without Characteristic Marks/ Qualities], Causality [pratyaya), Teaching the Cause of Buddhahood (buddha-hetupadesa), the All-Knowing (sarvajna), the Conquering One [or Conqueror] (jina), or the Will-body (manomayakaya).
"While I am thus known in hundreds of thousands of three-asamkhyeyas of titles, not only in this world, but in other worlds [too], my names are not exhausted; I am like the moon casting its shadow [reflection] on water, I am neither in it nor our of it. Those who know me will recognise me everywhere, but the ignorant who cannot rise above dualism will not know me.
"They pay respect and make me offerings, but they do not understand well the meaning of words, do not distinguish ideas, the true from the false; they do not recognise the truth itself; clinging to words of teaching they erroneously discriminate that the unborn and undying means a non-existence. They are thus unable to comprehend that one Tathagata may be known in many different names and titles." (Emphasis added; from The Lanikavatara Sutra, quoted in Studies in the Lankavatra Sutra by Dr. D. T. Suzuki, orig. ed. 1930; Motilal Banarsidass, Delhi, 1999, pp. 353-354).
Subhuti, the highest, most fulfilled, awakened mind that the Tathágata has attained is neither graspable nor elusive. This is why the Tathágata has said, 'All dharmas are Buddha dharma.' What are called all dharmas are, in fact, not all dharmas. That is why they are called all dharmas. (Diamond Sutra)
NOW FOR THE NIKAYA SUPPORT, Buddha has awakened to anything -- everything that has been or will be thought or attained -- this means all those sacred books written by men :
"Whatever in this world — with its devas, Maras, & Brahmas, its generations complete with contemplatives & priests, princes & men — is seen, heard, sensed, cognized, attained, sought after, pondered by the intellect, that has been fully awakened to by the Tathagata. Thus he is called the Tathagata.
"In this world with its devas, Maras, & Brahmas, its generations complete with contemplatives & priests, princes & men, the Tathagata is the unconquered conqueror, all-seeing, the wielder of power. Thus he is called the Tathagata."
all-knowing am I,
with regard to all things,
released in the ending of craving:
having fully known on my own,
to whom should I point as my teacher?
I have no teacher,
and one like me can't be found.
In the world with its devas,
I have no counterpart.
For I am an arahant in the world;
I, the unexcelled teacher.
I, alone, am rightly self-awakened.
Cooled am I, unbound.
To set rolling the wheel of Dhamma
I go to the city of Kasi.
In a world become blind,
I beat the drum of the Deathless.'