Continuous quantity concerns measurable extension, such as length, width and depth. Discrete quantity concerns countable multiplicity. Physical objects admit both measurements: a board has length and a stack of boards can be counted.
The negation of magnitude and number here is not a denial of divine unity; it excludes bodily units, quantitative composition and numerical multiplicity within the divine reality.
Example: A board can be three units long and ten boards can be counted. Saying God is one, by contrast, affirms uniqueness and the absence of a partner, not a measurable unit among bodies.