what happened here???!!

[amolitor]

Looks to me like one curtain or the other got stuck, and then unstuck.

It's a straight line, but it's not perfectly horizontal.

 

[Judobreaker]

Unless you perfectly corrected any distortion of the lens (which I highly doubt) I think this probably is not something outside the camera.
If it was the line would be distorted somewhat wouldn't it?

 

[KmH]

Don't forget that the lens projects the image onto the image sensor upside-down. So that less exposed strip was at the bottom of the image sensor.

The shutter curtains move from the top to the bottom of the camera so gravity can help them move downward to make an exposure.

That the strip is less exposed means it got less light, all of which supports the briefly stuck shutter curtain theory.

Situations like this is where understanding how your camera works on a fundamental level can be invaluable for diagnosing problems.

 

[CanonJim]

+1 KmH has it pegged. Intermittent shutter sticky.

 

[Stevedevil]

I would say that as the image would be inverted through the lens, then the second shutter was either sticky and too slow to react to gain the correct gap for the exposure, or too fast in creating the exposure gap that runs over the sensor, I advise altering the shutter speed up and down taking blanks, to see if its just a dust sticky issue..