But the health commissioner claims the decision was made on medical advice. Police logistics isn't medical advice.
It would make sense to circumvent the legal action by letting the public in on the secret advice.
This is an ongoing confusion/conflation. Doctors and epidemiologists aren't policy makers or population control experts. The medical advice is "we've found the virus is frequently transmitted where larger groups of people gather inside a house for a few hours, like when these idiots insist on throwing parties at night". It's then up to the government/police to come up with legislation and tactics to prevent these gatherings from happening.
So it's a policy or tactic created by the appropriate people in response to medical advice.