Like you, I wasn't there, so I cannot definitively say whether what you're saying is right. Injuries are most likely, as well as the Brumbies requirements, which can change quickly.
However, I will say that both have been great for the club this year - your implied message seems off the mark, like most of your comments about Easts.
Having soaking wet guys stick around post match exposed in the open in literally freezing (-2 to -4 degree wind chill) temperatures with strong winds and sleet will always leave you short. And, as mentioned, a shed load of injuries across the grades.