The absence of forward airspeed in this incident is really strange. It is SO hard to get an airplane to stop! About the only ways I know are a hammerhead (stall turn) and a flat spin. But there is no apparent rotational deformation of the airframe either, as you'd expect if it was in a flat spin. (No idea how fast a Baron would turn in a flat spin but the Pitts is going round about once per second).
I agree. No way a downdraught could have achieved this, IMHO. There is suitable terrain nearby but not that nearby.
Obviously it is possible to hit the ground with zero forward speed. What you do is a steep climb, to a stall, and then let the plane do a tailslide back down, and if you are really good you should be able to arrange to hit the ground in a flat orientation if you get it just right. Your VS will be pretty high at the moment of impact however - as clearly was in this case, with the wing spars thoroughly wrapped around the ridge.
I just don't think this pilot was doing that...
The domed roof deformation and the ejected seats must have been an oxygen cylinder explosion. Was this a turbo aircraft? Most of those have an installed steel cylinder of a fair size.