Who would have thought that a castellated nut and split pin was less safe than a plain nut and split pin!
From reading the report, it appears that it wasn't a conventional loop head split pin, but a dodgy home-brewed substitute made by sawing a cut in a piece of mild steel.
I'd trust my life (I probably have) to a properly installed split-pin/castle nut combination, regardless of the orientation of the bolt, although I vaguely recall from 40-odd years ago that CAIPs might have had something to say about the latter*.
Edit: *I've checked, and no they didn't