And yet, non-human animals CAN show definite kindness toward other animals - helping them when they are in trouble (eg. stuck in waterholes, or hit by cars, or otherwise injured, often at their own expense). They respond with empathy. And so I think the only reason it seems strange to apply the concept of kindness to non-human animals, is because WE as a species have never given proper attention and acknowledgement to this aspect of their behaviours.
Sometimes the sentences have references to books or films. I assumed it was to the Kind Dog book that was one of my favourites as a young child. Here's the only link I could find - maybe my mother should have hung on to it! https://www.amazon.co.uk/Kind-Dog-Monday-Angela-Banner/dp/0903368005