Crease marks for me, when I've gotten them, were narrower and either curved or slightly V-shaped. What you have there looks like it was caused by light, but I'm not too sure what would cause a spot in the middle of just a single frame like that. Light leaks from the camera body often extent to the edges of the film and light leaks from a shutter curtain would affect multiple frames.
As you suggest, it will be easier to troubleshoot if we can see the neg.