Theravada Buddhism is not a religion, but it is the minor sect of Buddhism. Mahayana Buddhism as espoused by Dhammapada and its multitude of Boddhisatvas IS a religion, and much more popular.
Original Buddhism as derived from Jainism is staunchly atheistic, believing there is no creator god, and the deities are just higher evolved beings also subject to karma.
Btw, Gautama didn’t reject Hinduism.
The Hinduism of today didn’t exist. The majority followed Vedic Hinduism, a Veda ritualized religion focused on purely Indo European gods like Indra/Perun/Thir/Tiw, Vasu/Vayu/Wiatr, Agni/Ogien etc and those gods are capricious.
Around 300 AD we see the current form of Hinduism, with a focus on personal gods like Krishna or Rama and the creation of the Hindu trinity: Brahma vishnu Shiva
Thank you for the clarification!