I still claim optical illusion.
Or, we can get more detailed. To quote from
StarDestroyer.net, we can either treat the movies as a Literary work or as a Suspension of Disbelief. If it's literary, it treats the films and TV shows as a mere "depiction", or "dramatic re-enactment" of a world which exists only in the author's mind. If we're going on a Suspension of Disbelief, we pretends that the fictional universe is real, which means that the films and TV shows are considered documentary footage and books are treated as if they were real stories, historical records, official spec sheets, etc.
I tend to treat issues like this using the former, which means that what we see in the films is subjective data. We concern ourselves only with what we believe the author's intent to be. Films and TV shows are considered a mere "visual representation" of the "real" fictional universe in question, which is assumed to exist only in the creator's head (or maybe it does exist somewhere else, but we don't have access to direct footage so we recreate scenes the best we can).
So in this case, the scene we see with the proton torpedoes executing an insanely impossible turn is in the movie because it looks cool, not because we're intended to actually believe that proton torpedoes can turn like that normally.
Or if you still insist on the latter, more literal approach, there's always the optical illusion. I like that one.
Incidentally, this is why I firmly believe that what we've established as the maximum speed for X-Wings based on timing them move down the length of a Star Destroyer is far beneath what they're actually capable of, but am willing to accept it due to limitations of the game engine, and as a limitation of the cinematic that were used to create the scene.