Maybe they weren't a military contract at all, and the country they were destined for requires a 180 degree rotation of the safety.
That means the original marking could simply have been fire. But since it would be in the wrong spot for us, they milled it off and just put fire in the usual spot.
I don't know of any country that requires such a thing, but the way those Colt AR-22 safeties worked is what made me think about it.
Another possibility is the machine was accidentally set up for the left side stamp and used on the right side. If you look at your regular rifles, on the left side, the E in SAFE is what is next to the hole for the safety. On the right side, the S in SAFE is closest to the same hole. If you swap the rifle end for end, you must also move the SAFE stamp to the other side of the hole so it comes out in front of the hole in both cases.