Weird, ain't seen a sheath like that before. Do the tabs at the bottom have snaps or are they just rivets? Does the stitching look pro or amateur? Given how uncovered the blade is it looks to me like it may be a matter of making do with leather scraps, but I could of course be wrong - on the other hand, it might simply be for someone who's using the knife fairly constantly, and only needs somewhere to safely pop it when they need to do something else, rather than somewhere to safely stow the knife for longer periods. Another thought, perhaps it's modified from the frog for a seperate sheath and knife. Interesting find though!