Why does Mrs. Barnett think it was black men who broke into the store?

Mrs. Barnett believes it was black men because they wore masks over their faces.

T.J. slipped through the window and opened the door, and the Simmses entered, their faces masked with stockings and their hands gloved. T.J., now afraid that they had something else in mind, wanted to leave without the pistol, but R.W. had insisted that he have it. R.W. broke the lock of the gun case with an axe and gave T.J. the much- longed-for gun.