It looks like a beautiful sub-adult that possibly picked up the scent of the skink that you were photographing at the time. Was the skink a Water Skink (Eulamprus sp.) by any chance, as RBB's seem to like eating them (if they can catch them!)
My pleasure Christine. I've seen a sub-adult red belly eat a juvenile bluey once, which is quite a chubby species (about equal to an adult water skink), so I think you're right that it could probably manage to swallow it if given half the chance.