Wow, what happened to Angus? i recall he had a boot in Vic champs but did not realise it was too serious injury..
Usually a moon boot implies a fairly serious foot problem. He broke one of his foot bones (I forget which one) at the Melbourne sprint weekend back in March and it hadn't yet come good. He rode in the Vic champs just to secure a spot in the team but was never a certainty to be fit for Portugal.
No, sometimes a moon boot means the clinician doesn't know what to do and says "2 months in this, then you'll be right." Patient can deal with the muscle atrophy later. I've got total body muscle atrophy, never seem to have been able to change that.
You're correct thought tRicky, usually a foot or ankle problem that needs minimal loading to heal.