If you think it's stupid, why post it? Lol, anyway, I think they would still be pretty thin under the bandages. After all, in the anime world, characters can be thin but really strong at the same time.
They're just normal arms. The bandages cover up the bruises he gets from training. I think its just Kishimoto think it wouldn't be Lee if he had big muscles under those bandages. Even if he deserves them. Its not a stupid question.