Cone count is my guess. Of the photoreceptors in the eye - Rods see in low-light and cones see in color. Some animals lack or have different cones compared to humans. Hence why bees can see "bee purple"
It seems to be a commonly used image stolen from Klaus Schmidt https://photographyoftheinvisibleworld.removed/search/label/bird%20vision but strangely none seem to have the lower bit. How odd...
Technically no, this photographer is putting flowers under a blacklight and photographing them, resulting in a picture of basically what a human would see IRL in that scenario (aside from things like contrast/exposure variances, etc). It's not really the same as what UV sensing animals would see. These photos are of regions of the flower converting UV light into human-visible visible light (via fluorescence, same thing as a blacklight poster). UV sensing animals are seeing actual ultraviolet being reflected by the flower as well as visible light, so it's not the same thing.