The strangest thing about this is that the organic cat litters are quite a bit more expensive than clay. So it wasn't done to save money. What the reason possibly could have been I cannot fathom.
Perhaps the brand they had been using switched to organic?
I suppose it's also possible that someone just assumed organic == better, or there were both organic and non-organic versions of the same cat litter, and a mix-up resulted when the premium product came up first in their search results.
If they'd known what the litter would be used for, I would hope they'd have been more careful, but I don't know at what level in the supply chain the decision to switch was made.