Two points:

1. You are making an argument based on labelling, not on content: That
is, the food going in to a pet food factory could well be 'human
grade'. However, it is *defined* as 'not human grade' by default, as
soon as it enters the factory. Or, in other words, the fact that no
cat food is 'human grade' does not mean that it does not contain
human-grade ingredients!

2. An exception might be Active Life food: They can in a factory also
used for human food[1] canning. I think they might be able to
genuinely label their food as 'human grade' on the basis of this,
although no doubt there's some possible semantic trickery there too.

In fact, on the Active Life web site, they have a large blurb talking
about 'human grade' and all that malarkey. They say:

'By definition pet food is not human food simply because it is labeled
and marketed pet food.
(...)
So, even if one uses only ‘human quality ingredients' but uses them
in a pet food only production facility, one is not making a human
product.  By regulation, the resulting product can never be labeled as
acceptable for consumption by humans because it was made in a pet food
only plant.
(...)
"Pet food made to people food standards."  This means that our Active
Life and Boulder Creek Farms canned pet foods could technically have
been labeled and sold as human foods up to the point where they are
labeled.  We choose to label them and sell them as pet foods.  The
ingredients and the production process are that of a human plant.  '

So, as you see, AL is, it would seem, truly 'human grade' throughout.
I'll also note that AL is astoundingly expensive, far more so than all
the other Touchy Feely foods.

Steve.
[1] That's food for humans, not food made of 'em.