Hoes are manufactured with both inside and outside edge bevels. The most authoritative guide I see on sharpening is from the US Forest Service and describes an inside bevel in all except one case.
Intuitively, I see the bevel placed on the inside of the strike radius to force material in the desired directon, like a spade. I realise that a wood chisel is used in the opposite orientation when cutting a slot (when the chisel is used with only a small angle to the grain of the wood), but finishing of the edges is done in the same manner as a hoe.
The question is -- why is there conflicting advice on the choice of edge orientation, and whether any actual difference informs this choice.
Update:
An ILO publication on Rural road maintenance training mofules for field engineers has an image showing the bevel orientation. An earlier edition (offline only) indicates that this prevents bounce during use.