I never assume a dog on a leash is under their human's control anymore. I've seen too many times where the dog pulls the owner with them in trying to approach another dog or human, while the owner struggles to contain the dog. I'm especially nervous when the dog is medium size or bigger, and the owner is of small stature and/or a child. A leash is not sufficient; a dog who pulls their owner and ignores commands to stop is imho not trained.