hands_above_head states that it is "not to be confused with" arms_above_head. What is the distinction? Both tags appear to have 300 images, with 91 of those having both tags.

At least I do not understand the distinction between the example images on these two tag pages, and the text descriptions are not clarifying it either.

I guess, if ones hands are placed on top of one's head, then the arms are still at the level, if not below head. But that's not much.

Well, okay. You can also have your arms above your head with your hands below. https://e621.net/post/show/2029117/anthro-arms_above_head-blue_eyes-canid-canine-cani