I think it´s just tradition for them to use chopsticks and japan is a very traditional country^^ but for the reasen that using chopsticks increasing your concentration i´ve never heared, but it could be possible cause to use a knife and a fork is much easier and if u use chopsticks u have to have a good reaction
When do you think people die?
When they are shot through the heart by the bullet of a pistol?
No.
When they are ravaged by an incurable disease?
No.
When they drink a soup made from a poisonous mushroom?
No!
It's when... they are forgotten.
~Dr. Hiluluk - One Piece