Secularism can mean a wide range of beliefs. A secularist might be a communist of fascist or a libertarian or a socialist or.....

How does race come into it at all? Religion is about belief and most religions welcome people of any race.

In American English, “race and religion” is an old-timey expression that’s typically used as a broad identifier in a melting-pot context, eg. “We are a nation of many nationalities, many races, many religions…” ~FDR

I suspect the comment means culture, which is frequently confused with race. But culture is also not uniform and will differ by individual etc.

Then maybe my other point applies. Secularism can exist within many cultures

Some people consider secularism a religion though.

Religion relies on assumptions that cannot be proven physically, secularism just avoids those assumptions (I say this as a Christian who finds secular biblical scholarship fascinating and helpful).

Do you mean an empiricism-only view? That has its flaws as you know.

Secular humanism has been accepted as a religion for First amendment purposes.

Non theistic Buddhism is still considered a religion.

Worldview might be a better term for us to use in understanding people's first amendment rights. And also the idea that there is no neutral worldview. E.g. "secularism" is directly hostile to many religious viewpoints, and to the degree that its proponents use it to oppose religion, secularism becomes a religion/worldview/belief system.