Verified in Chrome 60.0.3112.10 and Firefox 53.0.3 (both linux) as logged out user, first attempt to view source (or 'edit') on the Wikimania 2017 site. Screenshot included.Probably reproducible if you clear all cache/cookies and are a user without the appropriate privileges when opening source of such a page.
It's very debatable whether this is good behaviour or not. On the one hand, we're telling them "anyone can edit" when they can't actually edit that page. On the other hand, a welcoming friendly introduction the first time someone tries to edit could be appreciated even if they can't actually edit that specific page.
This seems like somewhat of an edge case since, generally, people arrive on articles through search engines or through links on other articles, and the vast majority of articles are editable.