He means be healthy methinks
Calories is basically it, but good ones. Look for clean protein and clean food in general, junk food is always a step backwards for mass, took me some years to realize that. I really like almonds since I don't eat meat all that much and they have mad calories and are really cost-effective. As far as protein goes you should probably look into something with fiber, I'm all about the BSN Syntha 6 if I'm just looking to supplement a bulk, but again, your gains really come from clean foods