Now, is it possible that the 45º scratches were made by a grinding process, with the wheel shaped and set at that angle to produce a wide shallow round-edged trough?
Having said that though, it's good to remember that handfiling was taught as a serious skill in days gone by. I remember my friends who went into "fitting and machining" (even the title gives equal weight to handwork) had to produce a 1" steel cube entirely by handfiling, and it had to meet very strict criteria for squareness and flatness. Even we in electronics were given some filing training.
The chappie in the Pathe film would have got into trouble with the teacher - he is filing back and forward, rather than lifting his file on the return stroke. Back and forth is good on copper, silver and other cheesey metals - it helps clear the teeth for the next forward stroke. But on hard steel like reeds, it rounds and wears the teeth.