From the text, it seems like motion blur to me. The text blur more horizontally. If it is out of focus, it should be all around.
Based on the ExIF data, 300mm with slow 1/6 shutter speed seems to be the issue even with IS turn on.
Lens: EF70-300mm f/4-5.6 IS USM
Focal Length: 300mm
Aperture: f/5.6
Exposure Time: 0.167 s (1/6)
ISO equiv: 400