In this study, the vertical vorticity of octupole metamaterials generated by nonlinear surface waves is investigated experimentally. An analytical model developed takes into account two contributions, one from the classical Stokes drift vorticity, and another one added to match experiments. The additional contribution is the Stokes drift vorticity multiplied by a dimensionless scaling prefactor. It is found that the optimal prefactor decreases as the wave steepness increases. When this additional contribution is set to zero, the dominant vorticity decay time closely matches the wave decay time. Overall, the results imply that both the Stokes drift and the additional vorticity contributions are necessary to characterize these octupole metamaterials.