Re: Box not required?
314.25(B) Exposed Combustible Wall or Ceiling Finish. Where a luminaire (fixture) canopy or pan is used, any combustible wall or ceiling finish exposed between the edge of the canopy or pan and the outlet box shall be covered with noncombustible material.
Because heat from a short circuit, from a ground fault, or due to overlamping could create a fire hazard within a fixture canopy or pan, any exposed combustible wall or ceiling space between the edge of the outlet box and the perimeter of the luminaire is required to be covered with noncombustible material. The noncombustible material need not be metal. Glass fiber pads commonly provided as thermal barriers within the ceiling pan of luminaires can be used to meet this requirement. Where the wall or ceiling finish is concrete, tile, gypsum, plaster, or other noncombustible material, the requirements of this section do not apply.
410.10 Space for Conductors.
Canopies and outlet boxes taken together shall provide adequate space so that luminaire (fixture) conductors and their connecting devices can be properly installed.
Going back to the installation instructions, You will find they do not except the canopy only as adequate space for terminations, And only a box would allow this requirement to be meet.