The website of the United States Powered Paragliding Association describes what could have happened if the carabiner had slipped just a little more:
This pilot was quite close to a catastrophic situation on two fronts. One, a significant bump that unloaded that riser could have caused the riser to come completely out, leaving the pilot spiraling uncontrollably down on the remaining side. Two, the carabiner has dramatically less strength and a strong updraft could break it.
Here's my question: was this picture taken during or after the flight? If during, then, sir, the people of the Internet thank you for thinking of us first.
Link (scroll down) -via reddit | Photo: Stefan Obenauer
My best guess: this was a staged photo, taken on the hilltop on solid ground, to illustrate common clip-in hazards, perhaps as part of an article/guide.
This picture was submitted to the USPPA site by one Robin Rumbolt, based on a hear-say story told him by one of his students, with an image found somewhere on the internets - so not a highly reliable source.
http://groups.yahoo.com/group/ppgbiglist/message/31616
Considering,m that it has a locking gate, I'm surprised that it does not have a notch in the gate that under load (like this) would prevent the gate from opening even if the gate lock had come unscrewed.
Given how important this is I would have either replaced the 'binder, or taped the gate.