Afternoon Alwaysgreen,Without trying to be a downer, the milestone may have been to sustain a $1 billion dollar market cap or be in the ASX 200 for 3 quarters (both excellent achievements).
It would be great to know exactly what the milestones were but I doubt we will ever be privvy to that information.
Personally, I thought it may have been for when a new BRN director, whilst at lunch with the Rob at the local brewery, did a handstand and drank a full pint without touching the glass with hand nor spilling a drop.

Agree, there is no way to know what , milestones were achieved, though thay could add more detail such as the option exercise strike price , not hard and let's shareholders know the extra cash in company's acc.
Regards,
Esq.