..., the diagram makes sense of it, though the spokes all the same way is still unexplained.
...
I can't speak for whomever did the work, but they might have been thinking that putting all spokes with the heads on the outside would mean that it had the same effect of putting the flanges a few mm closer to each other, making the spoke angle closer to perpendicular at the rim?
I never saw any hubs laced with all the heads on the outside until a few years ago when I occasionally saw a front wheel laced in a radial (zero cross) pattern.
The slip on rings that I added to my hub slide on from the outside, there is a thin flange on each ring that keeps the rings from going too far. The rings are held in place by having spokes on the outside (heads on the inside of the hub shell flange) that hold them onto the hub shell. If all spokes were laced with the heads on the outside, there would be nothing holding the rings on, thus they could fall off.
I am clueless on why the red shells are different than the non-red ones.