How can people be so Blind??? Look Carefully! That is Just a small Insect (a Bug) walking on the camera's lens! (or on the window that the camera is looking through, on it's inner side) How can't you see it? (you can almost see it's legs!) You can see that it's a bug by it's stability, a target outside the aircraft, like for example another plane would NEVER be so stable related to the aircraft's sight. This also explains why it looks so blurry, that is because the insect is walking on the camera's lens (or on the inside window) and therefore it's out of focus.
Probably it was a Night Flight so they saw it only through their IR camera and not from their aircraft's window. Test it, find a small insect and locate it very close to your smartphone's camera, see how similar it looks to what you see here... (The glow in the video is because of the IR camera).
Pilots can get wrong like any other human been, Many pilots crashed into the sea becouse of Spatial Disorientation, they got confused and thought that the sea is the sky. Also In 2004 Mexican aircraft pilots thought that they are following a UFO but later it turn out to be just some Oil platforms (in the sea below them) that they saw in their IR camera, search in Google for more information about that.
Probably they did some maintenance works on the aircraft on a hot day/night before it took off and some bugs went inside, this things happens!