You may be right, but I don't think so. Let me ask you to do this: picture yourself being beaten by this man, who was drunk, with a leash, with fists, and "raising his arm above his head". Is it possible you are not going to be injured to the point of felony assault? Yes. Is it probable? Very doubtful. I know it's a damn gray area between firm discipline and cruelty, particularly to an observer, however, given the fact that several witnesses stepped forward to denounce the guy, I'd guess he crossed it. Honestly, if he loved the dog, why wouldn't he petition for it back?
I could see a wide range of punishment for this guy, including an order that he undergo "obedience training" at his own expense or an order that he not own any animal for a period of years. But a felony conviction is way, way too much. You may not get a felony conviction for assaulting a HUMAN BEING, for heavens sake. (Simple assault or battery are still misdemeanors in a lot of states.)