You have to pick:

There's nothing here that indicates the litter box has been used yet. Whereas if a diaper has contents, it's probably been used.

It could just be the lining of the diaper, or whatever.

I suppose it depends on what the contents is...

It makes a difference if its clumping litter. Clumping litter you could just choke down the clumps without tasting them. But non-clumping you'd have to taste more cat pee.

If the contents are just air, hell yeah!

I think the intent is the contents of a used diaper. But perhaps it is better if the contents are unknown at the time of the choice. Maybe it is indeed empty. Or maybe not. Once you agree, you're committed.

I think that with a diaper, there's simply less volume of potential material to ingest, making it the favourable option.