He probably has similar genes to my husband -- he can work out (lift) for a week and get incredible muscle definition (regardless of diet). He is tall and thin (6' 4" and 180-195 depending) and very strong. He lifted regularly maybe 20 years ago but does not now. However, he, his brother, and dad all have this build -- very cut chest, arms, back, abs (although he does have skinny legs), and if he lifts even just a little, he looks amazing. Shoot, he works hard in the yard and garden in the summer (doesn't work out per se and gets more definition). He says it genetics, and I agree. Some people would have to work very hard to achieve that definition and be very strict with eating; others not so much.
This isn't fair, is it?!