my guess, as somebody who's jumped out of airplanes a lot and seen what the planes are doing while setting up for formation jumps, the pilot was either hot dogging it or not paying attention. One of the most important rules in skydiving (and thus in the supporting activities like airplane flying) is "Plan the jump, jump the plan!". Wake turbulence is stressed out on regular bases and is something constantly on the pilots and the jumpers minds. My guess is the guy thought it would be cool to get over the other plane and have his jumpers exit from there. In the heat of the moment he forgot about the turbulence and bernoulli's effect and got to close. What ever happened, I am 99.99% sure it is the fault of the trailing pilot that ended up on the top (guessing from the facts as they were presented in the videos).
pierre
