We show that fiber-delivered, pulsed laser propulsion of glass microspheres, as observed in a recent Letter [Opt. Lett. 36, 1996 (2011).], due to only radiation pressure cannot explain the measured maximum velocity of microspheres. Our considerations, based on the reported results, indicate that the main momentum transfer mechanism is due to mass recoil that very likely follows a dielectric breakdown near or on the surface of the microsphere.