I understand "ricing" to mean customising the appearance of a Linux machine, see e.g https://old.reddit.com/r/unixporn/top/?sort=top&t=month (SFW). So in this case I assume the UI has a cat theme or cat icons.

I think the etymology is from "rice burner" cars [0]:

> Riced out is an adjective denigrating a badly customized sports car, "usually with oversized or ill-matched exterior appointments".

[0]: https://en.wikipedia.org/wiki/Rice_burner