Many programs built around the barbell back squat such as Starting Strength and its child StrongLifts claim that squats will add inches to your arms faster than anything else. Similar statements, however, are deprived of logic.
You don’t need squats to develop strong arms regardless of what the 5×5 maniacs say. If you want your arms to grow, you have to train your upper-body. You cannot expect lower body exercises to take care of the upper musculature.
When you squat, your arms are not supposed to hold the weight. You don’t need strong arms to squat heavy weights.
There’s also a common misconception according to which squats make the body release extra testosterone and promote overall growth.
It’s been proven that the testosterone released after squats is not higher than the amounth released after ”smaller” exercises like bench presses, pull-ups, push presses…etc.
Sports like gymnastics are a proof that big arms are not dependent on squats. Gymnasts usually have big arms, chest and back coupled with a modest lower body development because the specifics of their sport require it.
Gymnasts rarely squat, although there are documented cases of gymnasts being required to squat 2 times their bodyweight. However, this is definitely not the norm, and many coaches try to limit leg hypertrophy to a minimum.
Having said that, good squatters tend to have bigger arms than the arm isolation crew because they understand programming better and focus on specific goals.
People who are dedicated to squatting heavy usually put more effort in the gym than the spoiled bros obsessing over arms day and night.
Ultimately, however, your arm size is determined by genetics, experience, training, nutrition and status (natural or not). Squats are not a factor.