It is correct. Your field of view will be different in the vertical axis vs the horizontal axis due to your monitor. You have a 90 degree horizontal (from your monitor perspective) field of view, but will have a narrower field of view in the vertical display direction because your monitor has a rectangular display. The aspect ratio of your monitor is 16:9 (horizontal:vertical), so you would expect a field of view to be 90 degrees side to side and (90 * 9 / 16 =) 50.6 degrees top to bottom. This leaves a gap of about 40 degrees between "cardinal" views in the vertical direction, and not a lot of overlap with the diagonal view either.
If the view were 90 degrees in both directions, your view would be distorted as the view would have to be 'squashed' vertically to fit.
Mike