I can't find any reference to 30 being the allowable number of visitors at that time. The public health order that seems to have been in place at that time allows for 100 visitors and even more subject to certain conditions.
Part 2 Residential premises 8 Directions about number of persons allowed on residential premises (1) A responsible person is directed not to allow more than 100 visitors to be at a place of residence, or more than 100 persons to use premises for the purpose of a holiday home or a short-term rental, at the one time unless—
(a) each visitor or person provides their contact details by electronically registering them by means of a mobile phone or other device at the time the person enters the premises with— (i) Service NSW, or (ii) a responsible person, and
(b) a responsible person— (i) has and complies with a COVID-19 Safety Plan that addresses the matters required by the approved COVID-19 safety checklist set out opposite the type of premises in Schedule 1, Column 3, and (ii) keeps a copy of the COVID-19 Safety Plan while the gathering occurs at the premises and makes it available for inspection by an authorised officer or a police officer as requested.
Extract from Public Health (COVID-19 Gathering Restrictions) Order (No 2) 2021
Commenced at the beginning of 2 June 2021
Ministerial Diection reduced number of visitors to 5 effective 26 June.
Division 2 Residential premises 9 Directions of Minister about number of visitors to a place of residence
(1) The Minister directs that each adult member of a household must not allow more than 5 visitors to be at the place of residence of the household at any one time.
Extract from Public Health (COVID-19 Temporary Movement and Gathering Restrictions) Order 2021
Can anyone provide information re the supposed limit on visitors of 30 at that time?
PS Not trying to nit pick just don't like the continual use of "illegal" when maybe that wasn't the case.