First, this is a wierd story. At first, I thought it was staged, because the action was framed so well in this "security" camera. But that aside, it just seemed so arbitrary and spontaneous (and mean).
That being said, I don't disagree with comments about how the coverage is OTT and that hysteria is being built. I can believe that the lady doesn't know why she did that. I've seen stuff like that before. And while what she did was certainly wrong in that the cat could easily have been killed, it wasn't harmed in the end.
But regarding animals vs humans, my personal theory is that pets like dogs and cats are very trusting. Just to be clear, this is strictly speculation on my part. To many people, the dog and cat represent unconditional love and loyalty. Harming an animal like this is akin to harming a small child, who shares many of these same traits. There's a naive loyalty and a stoicism in animals. They don't get mad when you're not there. They're just happy to see you when you are. They appreciate being scratched and hang out. They don't need much and appreciate what they have.
Much the same as a person randomly doing harm to a child, you have to be pretty despicable to randomly harm someone's pet.
As to why this is causing such a stir? I think it's because it was caught on tape and the woman was identified. You have a senseless act of cruelty. You have film of it happening. And you have a clear villain. It's tailor made for viral hysteria!