Lily from animove, on 24 March 2019 - 06:58 AM, said:
strange how did the game attach these to the legs or lower CT part XD
wonder if that can be used for funniy things like swinging a sword decal

This might
help. The video is about AI tricks, the specific presentation is about tricks for having AI clean nav-meshes.
But during the initial aspect, he presents a problem where you have an undesired "island" or aspect added into your nav mesh that you don't want because no player or NPC should be able to traverse there.
Here, think of it as less of a place where NPCs can travel and more of a spot that the Decal can attach to.
An unintended spot for it to attach to.
(Link is fast forwarded to the relevant part. If not, skip to 5:14 and let him talk for about 30 to 40 seconds.