According to the comments on the video, that wasn't Stevo jumping in IMC.
A little hunting yielded this rather straighforward account of the crash:
http://www.splatula.com/bfl/
Post#115
This report came from Simon Plume, a friend of Stevo's who was also on the load:
It was our 2nd jump for the day in the Litldahlen area. The first was from the 3rd valley, this jump was from the 2nd valley. The visibility was excellent, there was a small breeze at the exit point but nil wind down below. The jump is about 4550 feet from exit to landing. It was a 5 way, wingsuit jump. But due to the nature of the exit point, only about 2 jumpers can exit simultaneously.
Stevo exitted first, followed by another jumper and then myself with 2 others following. He was in a V1. We flew the left wall out into the valley and then turned a sharp left to follow the wall along to where the 3rd valley comes out (We have flown out of this 3rd valley on 2 other occasions - one being earlier that day). At this point, I was about 80m behind and slightly above. Stevo had planned to fly up into the 3rd valley briefly before coming back out. We were flying close to 90% max flight.
Stevo turned left into the 3rd valley briefly, before straightening again and then he started to turn right back out of the 3rd valley. I did not go into the 3rd valley but continued to fly straight. Due to his turn I was now only 40-50m behind and still above. As he continued his right turn it became a hard bank (most likely because he realised he was too far in) to the point that his right arm wing folded under, similiar to when you initiate a barrel roll. With the speed he carried into the turn he most likely would have been getting alot of side-slip as well. Stevo corrected but lost stability whilst trying to maintain his sharp turn. He remained unstable and impacted the far side of the gorge after another 2 sec. At this point I was about 30-40m above and 10m behind.
I flew away from the valley, opened, landed and we called a helicopter. Stevo's body was retrieved within 2.5hrs.
Note that the rest of the posts in that list are pretty much the same kind of stuff. Kinda like reading NTSB reports...informative but not a lot of fun.