Before you talk to him, think about the type of person who would treat their dog that way. Then think about what his response will be to you.
I had such an experience a few years ago. A house was being built next door to me. The property owners let some guy (looked like a Meth head) live in a camper in the back yard (maybe to keep an eye on building supplies). He had a large German Shepard that he kept tied to the camper with a rope.
I was driving about a mile from my house & saw that dog wandering around in the street - cars barely missing him.
I stopped & tried to call the dog to me to put him in my car & drive him back to the house. It took several minutes of coaxing because the dog wouldn't let me near him. I was scared of him, too; he wasn't the friendliest dog. Finally, he got in my car. I took him back to the property. The owner's camper was there, but he wasn't. The rope the dog was tied with was chewed off.
I didn't know when the owner would return, so I brought the dog in my house & gave him water & chicken.
I heard the owner's moped pull in. I brought the dog to him & said, "I found him wandering a mile away; cars were swerving around him."
Ya think he thanked me? Naw. He starts yelling at me: "Don't give me that s--t....my dog don't run away.....just get the f--- off my property."
I just left.