In reply to SCrossley:
Sounds like he may have been using a poor imitation of a "click-check"
Possibly with a self locking carabiner and assuming that when he hears it "click" shut, he assumes that the locking mechanism is engaged. In reality the click could be the gate contacting the attachment ring on the harness and the 'biner not secure.
A "click-check" should be a squeeze of the gate to check the locking mechanism has engaged and the carabiner cannot open. Always accompanied by a visual check that it is connected to the harness correctly.
All points regarding this individual case are supposition, of course.