Note that Screenhero was acquired by Slack; the "joined" label is an odd usage that implies that they just registered for the service.
Ya it is a bit confusing. I had to click through to "Read the Full Story" page to find out Slack acquired Screenhero.
A possible [January 2015] tag could be added here, because it happened a while ago.
I can't wait for the integration to be released, though. Then we can finally ditch skype for good.