Read the act yourself, there was nothing wrong with Scott Morrison making the decision:
66 Delegation by a Joint Authority for a State (other than Tasmania) or the Northern Territory
(1) A Joint Authority for a State (other than Tasmania) or the Northern Territory may, by written instrument, delegate any or all of the functions or powers of the Joint Authority under this Act or the regulations to 2 persons together, each of whom is one of the following:
(a) an APS employee who is an SES employee or acting SES employee;
(b) an employee of the relevant State, or of the Northern Territory, as the case requires.
Note: The expressions APS employee, SES employee and acting SES employee are defined in section 2B of the Acts Interpretation Act 1901.
(2) A delegation under this section:
(a) must specify one person as representing the responsible Commonwealth Minister; and
(b) must specify the other person as representing the responsible State Minister or responsible Northern Territory Minister of the Joint Authority; and
(c) must be signed by both members of the Joint Authority.
Note: See also sections 34AA and 34AB of the Acts Interpretation Act 1901.
(3) If the Joint Authority delegates a function or power under this section, the delegation continues in force despite:
(a) a vacancy in the office of responsible Commonwealth Minister; or
(b) a change in the identity of the holder of the office of responsible Commonwealth Minister; or
(c) a vacancy in the office of responsible State Minister or responsible Northern Territory Minister, as the case may be; or
(d) a change in the identity of the holder of the office of responsible State Minister or responsible Northern Territory Minister, as the case may be.
(4) Despite subsection (3), a delegation under this section may be revoked by the Joint Authority in accordance with subsection 33(3) of the Acts Interpretation Act 1901.
(5) If a delegation is made under this section, sections 59 and 60 do not apply to the delegates.
(6) If the delegates are unable to agree on a matter requiring decision, they must refer the matter to the Joint Authority.
(7) In the application to the delegates of a provision of this Act containing a reference to the opinion or state of mind of the Joint Authority, the reference is to be read as a reference to the opinion or state of mind of the 2 delegates of the Joint Authority unless they disagree.
(8) A referral under subsection (6) is not a legislative instrument.
https://www.legislation.gov.au/Details/C2022C00131
(20min delay)