The Buddha was born in a Hindu family in North India in the state of Bihar. He was a high caste Hindu and was born in a royal house hold. It stands to reason that in his childhood he was taught the Hindu scriptures and the basic beliefs of Hinduism like immortality of soul, rebirth, transmigration of souls and following the right paths including Ahimsa were imbibed by him.
No Buddhist will deny that these principles of Hinduism form the corner stone of Buddhist beliefs.
The Buddha thus preached nothing new and incorporated the same theories of Hinduism in his thoughts
The Buddha is also recognized in Hindu philosophy as the 9th Avatar of Vishnu, the omnipotentHindu God. Nowhere the Buddha denied this.
The Buddha lived at a time when Hinduism was still animist in its approach. He also incorporated Hindu Gods and Goddesses in the Buddhism. Thus the Goddesses like Hariti are derived from Hindu Vedic thought. This is not to deny that Buddha did not propagate anything new. But he stated everything within the ambit of Hinduism. The fact is that Hinduism is an ocean that incorporates many beliefs. and philosophies.It is in fact a way of life. Buddhist thought is also part of Hindu thought. The one difference in Buddhism is that the caste system has been done away, unlike in Hinduism where the caste is omni present.
The Buddha was born a Hindu and even after enlightenment never denounced any Hindu thought. This is the clue and despite assertions to the contrary, Buddhism in my view has nothing extra to offer, than what is already stated in Hinduism.