A childhood belief about general

When I was young, I saw some guys who were bodybuilders in the 80s and they had a lot of body hair. I heard my mom and some of my school teachers comment on them, saying, "Wow, look, they have a lot of muscles". I thought that "hair" only referred to the hair on top of your head, and that the word "muscles" was referring to their coincidental abundance of body hair. I asked them what "muscles" were, and they said that "muscles make you strong" and that I would get more muscles as I got older. I was with my Dad at the mall and saw a guy with a lot of body hair (not muscular though) and I said, "Dad, look- that guy has a lot of muscles!" and my Dad's feelings were hurt. He said, "Don't you think I have a lot of muscles?" he didn't have much body hair. I said, "I don't know." His feelings were hurt. One day, I grew a long hair on my arm and showed my Mom. I said, "Look at my big muscle!" and she laughed and said, "That's a hair!" and then I understood.