Wow that one is a real beauty! I love the slight die rotation on the clash as well. Keeps it interesting.
It's not known. Many folks don't think that just the die falling could cause it. The dies are really hard so there must have been some force behind it. This variety is also a DDO.
WOW! It took me a long time to understand exactly what a "clashed die" error was when I was a kid. If I'd seen that Kennedy, I would've understood instantly. Spectacular!
Here are a few clash dies from my son’s collection: http://www.pcgs.com/SetRegistry/Album.aspx?showcaseid=2045
I picked up this late die state Hungarian 1894KB 10 Filler the other week due to the die cracks on the obverse and the heavy doubling on the reverse, but when I got it in hand I noticed some nice clashing as well. Take a look under the band on the crown and you'll see clashing (at a slight angle) from "filler" with clashing from the 1 visible just under the cross. Since the denomination on the reverse is so heavily doubled, you can actually see the doubling in the clashing as well. Great die cracks at 12, 2, and 4 o'clock. The heavy doubling on the 10 is what sold me on this coin, even though I already had a nice example. Note the corresponding die clash through "filler" from the crown's band (also at a slight angle). The entire outline of the crown is actually clashed across the denomination here, but it's tough to photograph. You can see some of it clearly inside the 0 and in the field above the right edge of the R.