Sodium Chlorite vs. Chlorine Dioxide
Sodium Chlorite is a white powder, which dissolves in water.

Chlorine Dioxide is a gas. This gas also dissolves in water to some degree and gives a yellow color.

Sodium Chlorite is used to make Chlorine Dioxide in the laboratory.

I strongly doubt, that someone has sent you Chlorine Dioxide, as it is to dangerous to store and to send.