The 'Hide Communities' page in 'Edit Profile and Settings' says:
Choose which communities will appear in the Communities and Top Network Posts sections of your profile.
Hiding a community means other users will not see it in your Communities list or Top Network Posts. It does not, however, mean your activity is private.
Although this explicitly states posts from hidden communities will not be visible in your top network posts, the top posts tab on your network profile still shows posts from hidden communities. While technically this may not be incorrect, since the network profile doesn't list them as Top Network Posts, instead it calls them Top Answers and Top Questions, this is still misleading.
IMHO the text should either be changed to make clear that this settings does not affect the network profile, or (as I'd prefer) the network profile should be changed to not include posts from hidden communities.
(Before anyone starts pointing out, yes, I do understand my activity is not private. But that doesn't make the text on that page any less misleading.)