"Brahminical Hindus" is new concept I heard for the first time. From an academic perspective, I would more than likely challenge the word "hindu" being used as a religion name. Most religions are more defined/codified. At the end of the day its all a tool to manage power/people, boundaries or groups can be created with almost any data point. Your comment/observation just happens to define/declare one new type of boundary

And what about their traditions makes their religion not Hindu but makes the “Brahmanical Hindu” traditions Hindu?

The claim that there aren’t other religions is not true because a lot of lower caste folks have explicitly converted to Christianity and or Dalit Buddhism as promoted by Ambedkar who was the driving force behind rights for lower castes in India.

What do you mean by "Brahminical Hindus"?

From what I know, religions except Christianity and Islam are generally grouped under Hinduism for most things(marriage law for instance) and by default you're considered a Hindu(you can't be officially an atheist).