Reliable CFD prediction of gust-induced motion requires an accurate disturbance at the airfoil and a means of separating the direct gust loads from changes caused by body motion. This study uses a staged validation strategy to connect these two requirements for a rigid airfoil encountering a deterministic finite-width strip gust generated by momentum sources. Gust transport is first evaluated in an airfoil-free domain, including the effect of compensating for nonlinear self-advection. The heave and pitch implementation is then verified against analytical constant-load solutions, after which fixed-airfoil and no-gust calculations provide references for interpreting the coupled free response. Under the selected numerical conditions, the gust reaches the nominal airfoil location with amplitude and profile errors below 0.03%, an absolute phase error below 0.28°, and a convection-speed error below 0.11%. Self-advection compensation reduces the local profile NRMSE from 5.96% to 0.017%, while the rigid-body verification errors remain below 0.04%. The fixed and free load histories are initially close, but their maximum differences rise after the direct-load peaks to 0.0312 in incremental lift and 0.00200 in moment coefficient. Their subsequent reduction despite continued heave growth indicates a phase-dependent, motion-induced aerodynamic contribution. The airfoil is still moving at the end of the 1.00 s record; therefore, the calculation resolves the transient coupling pathway but not the final rigid-body state.