My limited understanding is there is a required notice period under FWA rules for an employee lockout. As such Qantas notified the Government of its plan to lockout employees in accordance with these requirements on the Saturday for a lockout on the Monday.
It then grounded the airline prior to this lockout even beginning. The reason for the grounding was apparently for safety reasons.
What were these safety reasons?
If Qantas had waited for FWA/Government to cancel the lockout due to national importance, the airline would never have needed to be grounded.