Or is a saintly log? Surprisingly good preservation is often cited in folklore and history as evidence for a) vampires and revenants or conversely b) the very pious, depending largely upon one’s social status. If you’re a peasant with retarded decomp, you’re a tool of the devil, whilst if you’re a dead abbot or similar, you might even get canonised.
The deceased tree member in question seems to have attracted the interest of the superstitious because the locals expect wood to rot underground or in water. Well, sometimes it does. Other times, not so much. It depends entirely on the conditions involved, included the levels of oxygen in the water. The fact that they equate the decay rate of wood with that of metal shows a misunderstanding of how things decompose. I’m no expert myself, but I would certainly consult one before leaping to the conclusion that I had a magical garden fence.