Comment on 'a slightly oblate dark matter halo revealed by a retrograde precessing Galactic disk warp' by Huang et al

Huang et al. (2024) measured the derivative of the phase φw of the Galactic warp traced by classical Cepheids with respect to their age τ and interpreted it as the warp precession rate ωφw/dt=-dφw/dτ. This interpretation is unfounded: young stars follow trajectories close to those of their parental gas and trace the instantaneous gas warp, not its shape at their time of birth: φw should hardly depend on Cepheid age. We show that the measured dφw/dτ>0 is consistent with an omitted-variable bias from neglecting the natural twist dφw/dR of the warp and the R-τ correlation for Cepheids (originating from the Galactic metallicity gradient and the Cepheid metallicity-age correlation).