I think that is fairly obvious. The observer mentioned Hezbollah was "swarming" their area. Unfortunately for the U.N. observers, Hezbollah miscalculated, like they have a tendency to do it seems, and an Israeli soldier on the ground near the post tagged it with a laser. Was it an honest mistake?, or did the soldier assume the observers were out of the area because of the enemy presence? Hopefully the investigation will find out the timeline and so forth.