It's an Occam's Razor thing. Why would someone purposely use a back-assword method of strap retention when people had been successfully using the usual soring bar for decades? My only reasonable explanation was that it was originally fixed-lug and someone cut it so they could more easily attach a strap... and trust me, I've had such thoughts mysellf at times! I have a wire lug "trench" that originally had a strap sewn on and believe me, finding something that looked similar enough was very difficult.
Believing this case came from the factory as you see it strains my credulity. But then, I've been wrong before, because some manufacturers in whatever field have come up with some wild designs in teh past....