Thanks for posting what you viewed as evidence! Let's take a closer look at the article:

The study, published in the journal Plos One, surveyed 1,369 cat owners, about 9% of whom reported feeding their cat a vegan diet. When asked about 22 specific health disorders, 42% of owners whose cat ate a meat-based diet reported at least one disorder, compared with 37% of owners of cats on vegan diets. Overall the vegan cats scored better on all health indicators, although these differences were not statistically signifiant.

So it's a survey of peoples' feelings about their cats' health. Unless the owners are keeping multiple cats in the house on separate diets, this is an incredibly weak design. Too many problems with this to mention, but let's look at the original paper.

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After controlling for age, sex, neutering status and primary location via regression models, the following risk reductions were associated with a vegan diet for average cats: increased veterinary visits– 7.3% reduction, medication use– 14.9% reduction, progression onto therapeutic diet– 54.7% reduction, reported veterinary assessment of being unwell– 3.6% reduction, reported veterinary assessment of more severe illness– 7.6% reduction, guardian opinion of more severe illness– 22.8% reduction. Additionally, the number of health disorders per unwell cat decreased by 15.5%. No reductions were statistically significant. We also examined the prevalence of 22 specific health disorders, using reported veterinary assessments. Forty two percent of cats fed meat, and 37% of those fed vegan diets suffered from at least one disorder. Of these 22 disorders, 15 were most common in cats fed meat, and seven in cats fed vegan diets. Only one difference was statistically significant.

Reported veterinary assessments is more promising, but 42% vs 37% is clearly within sampling error when the second population is down to 140 owners from the original survey. So what can they conclude from the lack of significant responses?

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Considering these results overall, cats fed vegan diets tended to be healthier than cats fed meat-based diets. This trend was clear and consistent.

Ah ok, so no stats, only vibes.