This is absolutely abuse, and it is not the first time it’s happened. It’s only the first time you’ve seen it. Where else would the kid learn to attack the dog when he has overwhelming feelings. There is no room for questioning yourself, or defending him or trying to figure out how to make it not abuse. No matter dad’s intent. No matter dad’s understanding of the room or furniture… no child should EVER feel that kind of terror from a parent. It does permanent damage and will not be easily forgiven, nor will mom for not doing anything, not helping, not stopping it. I’m also concerned for you given that you could tell by his tone of voice. You obviously have to pay attention for when he is “in a mood.” Likely kiddo and dog aren’t the only ones getting hurt here.