>how about the etymology of 'hoarding" in this connection?

good question. it's a different word, from the noun hoard which, for lack of a better description, is something akin to scaffolding.

1875 Parker Gloss. Archit., Hourd, Hoard, Hoarding, boarding used for protection...A term in military architecture for the wooden gallery, protected by boarding in front, which was thrown out from the surface of the wall in time of war, to enable the defenders to protect the foot of the wall.