I think you are the first one to even notice the walnut thing at all... I've had it for over a month now lmao
The use of nut shells(walnuts, pecans, peanuts), straw, clay, sand, and alfalfa for cat litter has been going on for awhile....seems to me there's another odd one I can't remember.(it's ground corn I couldn't remember) When my mom had 10 cats, I'd buy 50 lb bags of alfalfa from a feed store. Then ALL of the cat box went into the rose garden. Roses love alfalfa. It's a main ingredient in rose foods. So nothing thrown away. Nothing goes to waste. Even the times I used clay type (moisture absorbent) litters, I threw the stuff on the banana plants. I had fat bananas even in drought times--the litter collected moisture for the water hog tropical plants....I guess that 10 years of science I studied had some use after all.
edit: I should add a couple of warnings to the use of rabbit food (no additives)for cat litter. If you buy it from a feed store, make sure it's fresh and dry. Alfalfa will mold if moisture has gotten to it. And second, some cats will see that green alfalfa as a nice plate of greenery to eat. I only ever had one cat that ate too much and made herself sick. Green puke, green things in the litter box--ugg. She went to vet. He said don't worry, she won't do that again.....Still alfalfa is a good cheap litter.