I am not an expert but I have read about such practices again and again over the years. It´s also common knowledge that food companies do much, much worse things.
Dust is what remains after the tea has passed through the grading machine. It is powdery in texture and is often swept off the floor. Dust is considered the lowest grade of tea.
Diabolical but also logical, considering the strategy of starvation that has been going on for some time now.