The parent poster is more arguing that the atheist Jew label only really exists because most of the atheists in the US are Christian atheists to a certain extent (in that they celebrate Christian holidays and many aspects of Christian culture).

So you need to explicitly define atheist Jews as the exception.

Approximately 10% of the Israeli population identifies as "atheist Jews" (more than that are non-religious, but only a minority of non-religious people embrace the 'atheist' label)

I don't see how the identity of atheist Jews in Israel depends on non-Jewish people celebrating Christian holidays in the US (whether those people identify as atheists or not)