Well from what I’ve been told he thinks that the Buddha was some kind of kṣatriya supremacist on the basis of the few texts where the Buddha argues with brahmins about caste and ridicules them. But he takes these out of a context in the Early Buddhist Texts where birth-caste is understood throughout as irrelevant, and is subverted by the introduction of a notion of “moral caste” which is literally just equivalent to good character. So the Buddha speaks at length in various texts about outcaste-born people who he considers to be Brahmins because they refrain from killing and cultivate friendliness to others and brahmin-born people who he considers to be outcastes because they kill and cheat and steal. It just is not possible to reconcile this persistent understanding of character-based caste and friendliness and compassion being the virtues of good character with the racist warrior ethic Evola is trying to get at, I think, unless you do what I’ve been told Evola does, which is declare certain texts arbitrarily to not contain the true teaching and to be later additions.
There are ways to determine if something might be a later edition to a text, but only by comparing it with other versions of that text to see if parts are different in different transmissions of a story or dialogue. But Evola only looked at the Theravāda transmission of the texts he did look at, even where those texts had parallel versions in the Dharmaguptaka or Sarvāstivāda āgama canons (though he probably had no idea, since he wasn’t a scholar of Buddhism). Thus there is no non-arbitrary way for him to have decided which things are and aren’t legitimately early.
Here’s a thought about him from here https://www.reddit.com/r/askphilosophy/comments/j8f4yp/looking_for_critiques_of_evolas_revisionist/g8ajydb/
Evola was an individual who openly supported fascist ideology and actively involved himself with the german Nazi party. He admired himmler very greatly. When he talked about buddhism, he would over the time of his career attempt to unite it with fascism. Proclaiming that Siddartha was in essence a Nationalist Socialist and Shakya supremacist who upheld Martial beliefs and advocated violence. In this same regard, he also threw out the notion that buddhism itself ever advocated universal benevolence. This would include actively ignoring buddhist mahayana in japan and their vow to save all beings, in favor of highlighting japanese xenophobia as being the only form of buddhism existent in japan.
Evola imagines a buddhism that is violent, denies universal benevolence, has ideals of a noble racial caste vs the unclean lower castes while being kind enough to be open to those “worthy”. Funnily enough, Evola had also admitted he had no interest in buddhism as well. He only wrote it to balance his work on hinduism.