Rav Saadya Gaon translates ul'moadim in 1:14 as 'times', rather than festivals. (Tafsir there).
Rav Qafih explains (notes there) that rav saadya gaon's point is that holidays are not solely dependant on heavenly bodies. Rather, in his opinion holidays follow days of the month which are primarily defined by calendrical calculations.
Targum Onkelos similarly renders it 'times'. This is also the understanding of Ibn Ezra (there).
Furthermore, even if it meant that the constellations determine holidays, it could mean that the festivals follow the day of the month, but the months themselves could be based on the moon. Thus the moon is still the determinant. That is, the holiday would be some number of days after the new moon.