eastern spinebill

I was watching a yellow faced honeyeater's nest out of my bedroom window, which was hanging in an old apple tree. The parent birds had just begun feeding the newly hatched babies. I saw a bird land in a nearby branch but discounted it as my focus of interest as it was an eastern spinebill. It continued making it's way to the unguarded nest however. It poked it's long beak into the nest and continued thrusting it's head down in what seemed to me in quite an aggressive manner. Was it, or could it have been stealing nesting material in the form of down or existing nest material? Has anyone seen this behaviour?