Hard to say - especially when you throw in the possibility of translation from German. But based on the combination of details ("New stocking of a rifle gun", "new boring the barrel", but just "cleaning" of the outside of the barrel and the lock, screws etc.) it sounds to me like this was already what was left of a heavily used rifle when it was brought into the shop and given an overhaul and the barrel was rebored and re-rifled. ) Looks they rebored and re-rifled the barrel, reused the lock, restocked everything with new trigger and new mounts. The higher cost components (barrel and lock) were reused, resulting in what appears to be a fairly low cost in comparison with new guns of the day.
I find it interesting that the order was placed for a native and specifically required the gun be restocked and rebored as a rifle, not a smoothbore. So I would guess it was a rifle to start, but I could be wrong. If it were a rifle to begin with, makes you wonder how long it was in use, and where it came from, in order for it to need a complete overhaul by 1757. However, I guess with the heavy trade in deerhides, a native hunter could put serious hard use on a rifle in just a few years.
There is a another reference I have seen - might be from the same source - not sure - butI think it was the Christians Spring shope during the same general timeframe, mid-1750s or thereabouts, of them stocking a "rifle" for a "Shawanoe" (Shawnee) chief.
Guy