His chest and arms are not the best genetically and a few other weak points, but naturally you don't get much bigger than that. Having better muscle shape will make it appeal you're bigger, like Mr. Getbig, "Whateva" who has above average muscle shape and small joints.
Whateva is under 160lbs and 5' 8"-9" and he's well developed and been training for a long time naturally.
Being fatter will make you look 'bigger' but overall you'll look worse.