That’s utter bobbins.
The “natural” key is very often used on relations. Woods with holes in and lakes with islands are common examples.
Edit: I’ve changed this. The wiki is confused (quelle surprise) because it talks about “nodes”, “ways”, “areas” and “relations” rather than “points”, “lines”, “polygons” and “things with no geometry”. https://wiki.openstreetmap.org/wiki/Relation covers all relations, which can have various different sorts of geometry or none, and the first example given there is “multipolygon”, which obviously does have a geometry. It’s pretty meaningless to tag something with no geometry as “natural=wood”, for example, but a multipolygon “natural=wood” makes perfect sense. If someone wants to edit that page to say that “it makes no sense to use the ‘natural’ key on objects with no geometry” that would help further.