Part of your confusion may come from the fact that there were two separate actions.

On March 21, the government issued an Order in Council, Arms (Military Style Semi-automatic Firearms) Order 2019 (LI 2019/55), with the following short text:

For the purposes of the Arms Act 1983, the following firearms are declared to be military style semi-automatic firearms:

(a) a semi-automatic firearm that is capable of being used in combination with a detachable magazine (other than one designed to hold 0.22-inch or less rimfire cartridges) that is capable of holding more than 5 cartridges:

(b) a semi-automatic firearm that is a shotgun and that is capable of being used in combination with a detachable magazine that is capable of holding more than 5 cartridges.

The Arms Act 1983 already banned "military-style semiautomatic firearms". As an Order in Council, this measure could be taken by the government directly without waiting for Parliament to act, and was apparently meant as a temporary stopgap.

On April 11, Parliament did pass legislation, the Arms (Prohibited Firearms, Magazines, and Parts) Amendment Act 2019, whose (much longer) full text can be found at that link. This act also revoked the previous Order in Council which was then no longer needed.

Part of your confusion may come from the fact that there were two separate actions.

On March 21, the government issued an Order in Council, Arms (Military Style Semi-automatic Firearms) Order 2019 (LI 2019/55), with the following short text:

For the purposes of the Arms Act 1983, the following firearms are declared to be military style semi-automatic firearms:

(a) a semi-automatic firearm that is capable of being used in combination with a detachable magazine (other than one designed to hold 0.22-inch or less rimfire cartridges) that is capable of holding more than 5 cartridges:

(b) a semi-automatic firearm that is a shotgun and that is capable of being used in combination with a detachable magazine that is capable of holding more than 5 cartridges.

You can read here the Arms Act 1983 as it stood on that date. The possession of a military-style semiautomatic firearm was forbidden under Section 20 of that act, unless one held a firearms license with a special military-style semiautomatic firearm endorsement. So the effect of the Order in Council was to forbid the possession of all semiautomatic firearms matching the Order's description, except by the (presumably few) people that had been granted the special license. As an Order in Council, this measure could be taken by the government directly without waiting for Parliament to act, and was apparently meant as a temporary stopgap.

On April 11, Parliament did pass legislation, the Arms (Prohibited Firearms, Magazines, and Parts) Amendment Act 2019, whose (much longer) full text can be found at that link. I would rather not try to summarize the whole thing at this time, but one of its effects seems to have been to eliminate all references to "military-style semiautomatic firearms" from the law, and applying restrictions to a (presumably broader) class of "prohibited firearms". This act also revoked the previous Order in Council which was then no longer meaningful or needed.