Yep, the junk food means the ingredients comprise mostly of corn
/ rice fillers, and whatever little meat they have are meat
by-products (eg. chicken meal by product would include bone,
feathers, chicken feet, head, organs, etc.) which aren't fit for
human consumption, plus junk food have added colouring and are high
in salt which may cause urinary tract problems in the cats in the
long run.
The better brands are made with human-grade meat (cats need lots of
protein, even more than dogs), with very little carbo component -
they can be found at good pet shops.