USDA says that R. aquatilis var. diffusus is a synonym of Ranunculus longirostris: https://plants.usda.gov/home/plantProfile?symbol=RAAQD

How does iNat decide which "authority" to listen to?

The situation appears to be more complicated than it looks from as simple look at POWO. FNA lists both species as synonyms. Since POWO recognizes both R. trichophyllus and R. longirostris as accepted names, this represents a split in concepts instead of a swap. Based on the note here, it would probably be good for someone who knows how to differentiate these two to look at the occurrences in Mexico and the southern US as many are probably erroneously research grade under the wrong name as was the case here, here, and here.