The muscle was there on that guy, just under the fat. Those ads definitely show light/tanning/workout pump enhancements, but many of the dudes look like former college football players at 25% bf. Many 30-something slobs who have let themselves slide still know how to train if they did in their teens/twenties. If you work at a job where you use your arms every day, they will grow. If you use your legs, they will grow.
Again, I went from 235 lbs to 185 lbs in two months. My jeans size went fron 36 waist to 28 waist. I ran alot - and hardly slept. I didn't use any gear, but the low bf illusion is always there - you look bigger when your leaner.