I think Grant can't throw the ball hard because his shoulder is Raggady Ann. Also, from pictures I've seen of Grant in the past, I think he might have been in to body building a little more than football. 
Necks don't get this way naturally.
grant's never been into bodybuilding. everything he's ever done in the weight room is to make himself a better football player. his neck looks like that because he never skips a single set of neck iso in the weight room like 99% of football players out there.
trust me fella's he's not really that big, 6'1" 205-210 lbs. he eats a clean diet and works out (running, lifting and throwing, not just curls) constantly so he's got no body fat.