Was your friend male cat being fed dry only?? Cats should have some canned food daily to aid in the prevention of stones, some animals are genetically disposed to being stone formers the performatirin Ultra contains cranberries which is used to help the cats uninary ph in the neutral zone to aid in preventing urinary stones. The food also contains methionine which is an acidier which will help prevent struvite stones from forming the common type in cats and dogs but if this cats had the very rare type of stone calcium oxalate which forms in animals and people who have highly acidic urine then methionine would be a bad thing.
Now for the liver issue
There is no ingredients in the performanance ultra that would cause this kind of major health problem in a healthy cat. What I would highly suspect is contamination of the kibble by molds or bacteria. It happens every so often with dog food and a bad batch is shipped and suddenly several will be sick or dying, the last big incident occured in Diamond foods the corn they used had very high levels of alfatoxin( a mold that grows on corn) several dog in the eastern states started dying of liver failure, some people had multiple dogs that all became ill, because more virus due not impact the liver the state university who was treat several dog from multiple househouse started asking questions looking for a common link, which lead them to the dog food and test verified it.
If you have some of the food left, talk to the vet about having it tested for fungal toxins, if there is contamination make sure the company who makes is contacted, so they can check to batches and don't throw out the bag because this has the lot and batch number as this become evidence incase of medical claims in the event of a recall.
Toxic molds can develop in pet foods in your home as well, light will destroy natural preservatives in food very quickly so after opening it is important to make sure the bag is folded closed after each use, it is preferable only have enough food on hand for a couple of weeks, if a bag has been open greater than 4 weeks, it should be thrown out. You should not dump food out of the bag into plastic storage container, put bag and all into the container to prevent bacteria dangers. Food should be keep in a cool dry place, most kitchens have too much humidity to store food safely and can cause mold growth in foods. This time of year with the hot and humid weather pet foods can spoil super quickly if you don't have cental air to reduce heat and get rid of the excess humidity. Depending on the type of mold and quanity some pets may go off the food and do some vomiting in other types it can destroy the livers and be fatal