As per an external fact checker, the Ministry of Defense had stated that the Independence Square was decorated with Buddhist flags on 2nd February for the all night pirith chanting ceremony that customarily happens as part of Independence Day celebrations and the Buddhist flags were replaced with thematic flags designed specially for the Independence Day Ceremony afterwards. The said thematic flags were visible in the actual footage from the Ceremony as well. Read the explainer from the fact checker here (Sinhala): https://srilanka.factcrescendo.com/2021/02/04/explainer-on-why-buddhist-flags-were-used-at-the-official-independence-day-festival-location/.