I'm no accident investigator, and who knows how many factually details will come out. (perhaps someone was on frequency and heard some transmissions).
From the photo, a couple things stand out. There doesn't seem to be too much damage to the gear that is folded in. Tires intact, not twisted or sheared in an abnormal direction. The gear door is partially open, and there is some fluid present, but that could have come from the nacelle. Also they are still on the runway, a bit off centerline but it's possible they may not have even taken out any edge lights. As stated the lack of blown slides and no evidence of post crash fire show either the cabin experience was benign, or that they were hoping some nice fella at Oman air would just DDL the left main gear and engine and allow them to carry on and minimize delay.
It would appear to me that it was known before touch down that a main was not down and locked, and it was flown accordingly, and then at a slow speed the left wing finally stopped flying and that pulled them a bit cockeyed. If so, I would say well done.
Now, to the supper guppy pilots, any specifics on the gear system, gravity extension, is it possible to shake or yaw the plane and let springs and the over center locks to snap that main into place?