Phone the ASPCA and/or local animal control dept. and file a complaint. Take a photo or video with your phone if you can as evidence.
No dog should ever be treated like that. There are better ways to train a dog than that approach.
About 10 years ago I used to have a very hyperactive and unruly Springer Spaniel. I went to a dog trainer that our vet recommended and the guy was an ex military dog trainer from S. Africa or England. He had a similar approach which was rather abusive and offensive to me. Never went back.
Good on you for standing up for an animal who is being mistreated.