We previously reported that giant crystal enantiomeric excess (CEE) can be obtained when sodium chlorate (NaClO3) chiral crystallization from a solution is induced by the excitation of localized surface plasmon resonance (LSPR) of a Au triangle trimer nanostructure by a circularly polarized laser. However, the role of the LSPR excitation in the giant CEE remains unclear. In this work, we showed, by finite-difference time-domain analysis of plasmonic near-field, that the magnitude of a chiral optical gradient force originating from the strong superchiral near-field at the Au trimer nanogap on a virtual NaClO3 chiral crystalline cluster is comparable to that of the electric-field gradient force in previous laser-trapping-induced crystallization from unsaturated solution. We revealed that the giant CEE resulted from a difference in the frequency of attachment of chiral crystalline clusters to crystal nuclei or in the local concentration due to chirally biased diffusion rather than enantioselective optical trapping.