What are display and pixel width reported by mkvinfo?
The pixel values refer to the actual number of samples stored per frame. The display values refer to the dimensions that the player should render the video at. The ratio of 853/704 = 1.212 is the pixel or sample aspect ratio. This is an example of  non-square pixels, a legacy of analogue video signals and usually seen in digitized forms of NTSC/PAL format signals.