What is the reason for him keeping his arms so wide?
To lower his upper body so he didn’t pop straight up when coming out of the blocks. His arm position got progressively wider as his power levels increased.
I’ve found that having my arms too wide at the start I lose my smoothness in the ‘sweeping’ of the arms and driving from the start. I prefer a just inside the shoulder width. The end result is a smooth drive in a straight line. I’ve seen a lot of guys in comps with their arms wide and all it does is causes them to ‘skate’ from side to side which as u all know wastes too much time. 
The hand position controls the height of the shoulders over the ground, which will lower the departure angle and allow an extremely strong athlete to use all his back strength. For athletes with less power, a position with the hands straight down from the shoulders will raise the centre of gravity to allow an easier transition to the full upright position.
Charlie, did ben use any of his tricep+chest+shoulder power and strength to push himself off the ground during his start?
Ben did not push off the ground with his arms! The arm action is forward and back!
Thanks