I don’t have a lot of context around this issue either as I don’t subscribe to c/vegan, but one could make a compelling argument that stating a claim which is at odds with science as being fact (rather than stating something like ‘I believe (or ‘These sources say’) that feeding cats plant-based diets is safe, but these sources disagree’) is in itself disinformation. Stating a disputed thing as fact is at the very least misleading, and when it’s dealing with the health of animals, that probably should be enough to attract scrutiny.