The central teaching of Buddhism revolves around one single concept 'nirvana'. In this state you become one with all, rather you understand your true nature as the supreme self. While Hindus described this state as basically "everything", buddha and later many prominent buddhists described it as "nothingness" which appears as inconsistent with each other and hence folks might see Buddha as some kind of rebel. Buddha and Buddhists talk about "un-atman" and Hindus talk about "atman".

There is one major difference between Buddhism and some schools of thought in Hinduism like Yoga or Bhakti. While Yoga and Bhakti insist that a 'deity' helps you make the progress much faster on path of self realization, Buddha did not explicitly support this. He instead focused on more inward looking approach of meditation and contemplation (which is a subset of Vedanta philosophy in Hinduism). This is often seen as Buddhism being an atheistic philosophy by Hindus.

Both Hinduism and Buddhism allow its followers to embed this central concept into various other "decorations" and "facades". Which may involve supernatural elements. But they are mostly irrelevant for you to be either Hindu or Buddhist. This is in stark contrast to Islam, Judaism and Christianity where some central core beliefs absolutely require you to believe in supernatural elements.