Siri finds images in Photos even though search has been disabled - iOS 11.4.1

I was demonstrating Siri yesterday to my friend, showing how it can search the internet for random images (show me an ***image*** of a chickadee, a Volkswagen GTI, Albert Einstein, a pressure cooker, etc.) and it was pulling images from the web until I had it search pit-bulls using the phrase "show me a ***picture*** of a pit bull." Siri found and displayed images of my 2 pit-bulls _from the Photos app on the iPhone!_ It would not find any images when I searched using the dog's names, however. When I tested this same search phrase with "German Shepherd" it found images of three other dogs in Photos, which are shepherd _mixes_, not pure breeds. Most of the selected images were basically face-on (two eyes looking at the camera, floppy ears, etc,) but some are from the side and it found them even though pit #1 has a narrow face, pit #2 has a block-head, and none of the shepherds have the typical erect ears. I know that facial recognition is pretty far advanced in iOS, but I had no idea it could recognize dog breeds, and I was amazed that using "show me a picture" searches the Photos app. What is more disturbing is that I deliberately set Siri not to search inside the Photos app: Does anybody have a clue what is going on? I realize this question may be interpreted as a 'why Apple does something' query, and I will accept a downvote or two. I'll delete the question if folks think its immaterial in the long run. I'm mystified.