The Wikipedia definition seems to indicate it has origins as a racist term and I’ve never understood why unix users have adopted this terms instead of something benign like “themes” or “theming” which I remember being in use long before I ever heard “rice”. So what gives? Why use “rice” instead of “theme”?
The term comes from car modifications, when people would modify Japanese cars. Folks called them “rice burners” and it evolves from there.
I have never heard this in the Linux community, though, so it might just be a you thing