I believe the nozzle can impart a speed (velocity) to the droplet, and that it would correspond to the boom pressure.  It’s just that once the droplet is through the orifice and out the nozzle it is at atmospheric pressure,  it it can still have momentum/speed.  And the droplet is going to be affected by drag, or various aerodynamic forces, due to prop wash or turbulence or wind or foliage displacing air as it stands back up after the sprayer rolls through.