Any counter example that allows to eat non vegetarian food on a festival day can be an answer.
Yes, I am providing one counter example.
Durga puja is the greatest festival of Bengal.Raghunandan Bhattacharya, a renowned smarta pundit and the writer of the Ashtavimshati-Tattva compiled the vidhis of Durga Puja which is followed here. He prescribes that many animals should be on the Mahanavami day to Devi. I quote from Swami-Sishya-Samvad written on Swami Vivekakakda by His disciple Sri Saratchandra Chakraborty:
During the first Durga Puja at Belurmath in 1901, Swamiji asked His disciple Sarat Chandra Chakrabarti to bring one copy of Ragunandan's book on Durga-Puja. After reading the book, Swamiji says to Saratchandra:
If possible, we shall perform the worship of the Divine Mother this year. Raghunandan says: navamyaam pujayet devim krittva rudhira-kardamam (on Navamai tithi,Devi should be worshipped by creating a mud of animal blood). If the Divine Mother wishes, we will also do that.(Swami-Sishya-Samvad, Saratchandra Chakravarti,Udbodhan, page 229).
But the sacrifice did not take place because of Sri Sarada Devi's objection