I dealt with this a lot at a hosting company I worked for. This is almost certainly a .htaccess file that is set to only redirect based on referrer. It is normally under several hundred blank lines, to make it look empty to the casual observer.
I can't access the linked url (it's https: http://news.ycombinator.com/item?id=3575029), but as far as I remember, if an HTTPS page links to (or redirects to) another page that is not on the same domain, the HTTP REFERRER field will be empty.
We (nodejitsu) sponsored NodeSummit, but have no control over nodesummit.com. I have reached out to Charles Beeler (the conference organizer) to make him aware of the issue.