Wrong. CO2 used to be on certificate so that bit of law simply moved them into the category of air guns without FAC requirement unless suitably dangerous, ie over 12ftlb/6ftlb
I think that is what it says, CO2 is changed to being considered in the same category as an airgun but no other gasses are given the same dispensation. I do not understand why you are saying it is wrong since it is quite clear.