Using excitation of a high-quality passive cavity with sub-Poisson laser radiation as an example, it is shown that the effect of photocurrent shot-noise suppression below the quantum limit is not uniquely related to the magnitude of intracavity photon fluctuations when light is observed at the output of this cavity. Complete suppression at near-zero frequencies may occur for both ξ = -1/2 and for nearly zero values of the Mandel parameter, depending on the relations between the Q-factors of the passive cavity and the cavity of the sub-Poisson laser.