I think you're seeing a shadow/dark part of the pin. you c.an clearly not see "through" the part that i'm assuming you're saying is not closed. I think the pin is discolored there as a red herring.

It appears that there's a dark line on the clasp too, that you can see near the end, which makes it look like the pin part has been cut off.

My guess is that the horizontal clip is welded closed on the pin side, and then cut along the top part in the middle, the flick opens the cut temporarily. Either that or the same thing with the vertical clip's curlicue, it's cut on the back side that we never see. Everything's moving so fast and it appears like there's stuff planted specifically because it's going to be scrutinized.

But i'm pretty sure one or the other clip is welded shut on the pin side. mostly sure.