He belonged to Sakhya clan, Kshatriya. But his genealogy as gleaned from Buddhist texts indicate his ancestry goes back to one of the first Rishis after whom the gotra system of Hindu lineage springs from. The rishi is Gautama and he was a Brahmin .
More important is the fact that Silappatikaram refers to Buddhism extensively. This implies Buddhism,The Buddha should be dated 11,000 years back.
“The Mayavada philosophy is impious. It is covered Buddhism. My dear Parvati, in the form of a brahmana in Kali-yuga I teach this imagined Mayavada philosophy. In order to cheat the atheists I mislead them by describing the Supreme Lord to be without any personal form or qualities.”
But there are some well meaning people who do not understand Sanskrit propagate Hinduism do more harm to Hinduism than good. One such is a piece in Quora where the author states that Lord Rama called Buddha a Thief! And the article quotes Ramayana of Valmiki.
These systems which decried the excessive rituals( Justifiably so) of Sanatana dharma ended up with Rituals. They decried idol worship, landed in worshiping The Tirthankara, Mahavira and Buddha! Yes, to an extent the statement that Hinduism is like a Black hole in the sense it sucks the best out of every system and assimilates it. The reason is that while other religions were founded , had a founder and an intention to have followers.