Because you went from a https site to a non secure one (http://sbjs.rocks) so the referer header was hidden.
See: https://en.wikipedia.org/wiki/HTTP_referer#Referer_hiding
See: https://en.wikipedia.org/wiki/HTTP_referer#Referer_hiding
<meta name="referrer" content="origin">> Your source is news.ycombinator.com
Though it is noted in the usage:
> When a visitor come from https web-site to http, a request doesn’t have a referer.