Can someone be hindu and a Atheist?

[Dionysius]

There is a Hindu tradition that is atheistic. It is known as
Sāṃkhya

The system rejects God, gods, creator gods and personal gods. Instead, much like Buddhism it distinguishes a true reality from the false reality presented to us by the sense and the conclusions stemming from these.

Here is brief functional description of the system,

Sankhya and Vedanta

The only problem is whether Samkhya - or even Vedanta for that matter - can be called "Hindu" traditions - with Hindu meaning a religious identity rather than a cultural one? Hindu religious revivalists had the bad habit of putting the stamp of their religion on anything and everything they could see as originating from the Indian Subcontinent.

Hindu = Indus dwellers or those who dwell by the indus river or something like that. Insofar as Sankhya it bears the stamp of hinduism - it uses their religious symbols it just removes the superstitious aspects.