This isn't really what the above poster was saying, but "secular Jewish" can also refer to practically nonpracticing ("atheist" or "agnostic") or even practicing a different religion entirely. Since Jews are an ethnoreligious group, the identifier often refers to people with a Jewish ethnic background, vs people who are Jewish as a religion.
No, it's more about ethnicity and religion being intertwined. Judaism also references an ethnic group historically tied to the practice of the religion, but not necessarily. If you want to talk about people who are "ethnically jewish" but not "religious jewish", you can say something like "secular jewish" or "nonpracticing Jew".
I am a nonpracticing Jew myself. I don't identify with any of the religious or cultural aspects of Judaism (although I have some educational background). But as a Jewish person, I'm still eligible for citizenship of Palestine/Israel (though not interested for political reasons), and also eligible for targeting by white supremicists/neonazis
