Grandpa seems a bit rough, but it is because of the fact that he is living in Russia's cold winter with a dangerous wolf running about and a grandson who thinks he can best it with a popgun.
Grandpa only appears toward the beginning of the segment. He stops Peter from going off to find the dastardly wolf with a popgun, spanks him, and tells him that if he tries to go after it, he could very well end up getting eaten. To scare Peter further, he makes a wolf's evil fangs from his beard to show him the shadow puppet of the wolf on the wall. Peter turns around and tries to shoot it, but tricking him, he easily grabs Peter's cap and popgun from him and storms off. However, when Grandpa falls asleep in his chair by the fireplace, Peter manages to get his things back and sneak outside.
Trivia
In the children's book based off of the segment, it is revealed that after Peter returns, having successfully captured the wolf, Grandpa is pleased with him and glad to see his grandson safe, despite his disobedience. Peter also promises to listen to and never disobey Grandpa again.