We saw a fifth wheel that had done the same thing up in Paso Robles. The truck was, apparently, attached correctly - it was hanging from the upsidedown trailer.
I didn't get photos of THAT one, but check this
out. Or this
. Or this gooseneck version
And my favorite - in which the entire fifth-wheel assembly tore off the trailer
(this one's a commercial trailer, not a house trailer).
So...don't think you're immune just because you've got a 5er!
Speed, load and the side of the road, Baby - a bad combo with ANY rig.