My Ben is also not overweight, never has been, nor is he b&w, but he is persian, and that was another susceptibility pointer in that study apparently. He also not a stressy cat, and didnt appear to me to be stressed at the time. He had a couple of bouts of cystitis at the old house a little while before I moved (I was stressed!) and didnt have the blockage until the May after I'd moved in the January, so my guess is he was picking up on MY stress and other things that go on with a house move and the settling in to a new home.
As Den said, diet isnt the only factor, but Ben, at the time, was eating dry food only (I'd somehow got taken in by the whole dry food thing - before that I'd always fed wet food, never ANY dry), so that probably was a contributing factor in his case. The stress they feel isnt necessarily a tangible thing that we observe, its something they feel but don't always show - until something like this happens. And stress is different things to different cats, one cat may not bat an eyelid at, for instance a door being slammed, whereas another it would send its stress levels soaring. On the other hand, a life with too few challenges in it can be highly stressful for some cats.
I feed a raw diet as well as high meat content pouches, trays etc Applaws, Hi-Life, Forthglade, after researching the condition loads. They all do have some dry food, but just as treats.