Legal definitions are meant to be practical, in a very specific legalese way that's not necessarily literal.
A court ruled that discrimination against Jews fell under racial discrimination protections -- not because Judaism is a race, but because anti-Jewish discrimination is functionally similar to racial discrimination. By having one category, all of these groups of people can be protected as new legislation is added. Otherwise there would need to be legislative changes for each group. (This was 19th century, homophobic violence has forced a broader change, and it was a hard fight.)
So legally, it's quite simple to afford atheists protection for their beliefs about religion IF and only if it's called a religion. Otherwise, in the U.S., it would be a political nightmare.
OK, I'm done being a geek. Hi, Markyyy. No hugs for you today. x