Yes it is. At least true Buddhism, unless you mean the sort of bastardized Buddhism that dissatisfied Western kids on the internet arrive at after skimming through two sutras and a Wikipedia article. There are even spiritual deities and bodhisattvas in Buddhism which are revered via elaborate religious ceremonies. There is still belief in reincarnation and virtually the entire metaphysical system of Hinduism. Sure you can deny Buddhism's very context, history, and testimony of its believers, but you'd essentially be no different from the Protestants who say that Christianity isn't a religion because they deny the 2,000 year testimony of the Church, history, patristics, and canons.