You can see from the video that the slope is in and out of cloud which is quite usual in the mountains - it is entirely possible they entered cloud inadvertantly and elected to make a turn to recover VMC - perhaps they turned the wrong way or there are wires and cables (its a skiing area with lots of lifts) in the 'safe' direction towards lower ground.
As to why they were there - that's what they get paid for - again, normal protocol would be for the MR/ski rescuers to get the casualty to the cloudbase for extraction by helo.
As Jim will doubtless confirm - a bum leg can mean anything from a twisted knee to a femoral bleed so you err on the side of caution and get them to hospital smartly.
A very sad accident but it does look like CFIT in whiteout conditions - for those that haven't been there, it is bloody scary since you don't usually have an IFR pull-up option.