Not an uncommon practice way back when. The peep was employed as a light focuser to enable a crisper sight picture with the open sights. It works for that but slows target acquisition to my way of thinking. Why not just use the peep sight alone, and be done with it? I suppose it was done by guys who just couldn't wrap their brains around how an aperture rear sight works.
The same system is found on some upscale European rifles from a couple generations ago- spring loaded flip up "lollipops" in the tang, with a peep hole for the aforementioned light focusing. People often think they're peep sights but they're not.
