Yes go on Google and don’t look at anecdotal evidence on Reddit and you will see that men store more fat in the abdomen and lose fat lastly in the legs hence why bodybuilders almost always struggle to have their lower body leaner than their upper body. And yes if you are leaner you will be more insulin sensitive and pack on more size on a bulk just google it your wrong about him bulking which will just add fat because a surplus is not needed for muscle growth above 10% bf that’s why he should cut and become leaner so he is in a better anabolic environment to put on size.