My 3 year old has started copying the way a classmate talks

There's a boy in his preschool class who speaks very differently, short sounds and a lot of repeating. I don't know why and it isn't my business. But my son has started making the same sounds at home, on and off, and laughing. I don't think he means anything by it. He copies everyone, including me on the phone. I just don't want it coming out in class where the other boy or his parents could hear. How do you talk to a 3 year old about this without making the other child sound like a problem?