The chemical weapon used to gas the Kurds was a type of chemical weapon different from what Iraq had, although it was the same type as that which Iran had.
Also, no evidence was provided which would support that Iraq itself was at the cause of that, when in fact it is possible that Iran could have used the chemical weapons themselves in an attempt to discredit Iraq, or make it so that the Kurds hated/disliked Iraq/Saddam.

Fear my worthless info.