Pre-exposure would leave a dark mark on the film, and a light mark on the positive. What you're seeing here is either missing emulsion, deformed emulsion, or a deformed film base. (The latter two might cause the light to be deflected, leaving a dark spot during printing. The first would simply allow light through, leaving a dark mark.) Since it's dark on the print, it isn't a light leak or any other type of light strike.
Beats me as to what it is, though. Developing an unexposed sheet from the same box would show if the same defect appears. You said you shot film in other holders the same day, but not whether the film came from the same box.
Let us know what you see when you look at the negative.
Be well.
Dave