The OP cites a gay blog. Here is the news article which was the source for the blog post.
*Warsaw’s main boulevard, Marszalkowska, and neighbouring areas turned into a war zone on the Independence Day March on November 11. Row after row of mostly male youth marched along the boulevard spilling into sidewalks and side streets.They carried flags with Celtic crosses and white power fists, chanted slogans with visceral force and filled the centre of the city with fire-cracker smoke. The parade, with the number of protesters set at around 15,000, was organised by two of the most prominent far-right organisations in the country, the All-Polish Youth and the National-Radical Camp.
Few passers-by dared to stick around and watch the spectacle.
Within one hour of the start of the demonstration, participants had attacked two squats in the centre of Warsaw (Syrena and Przychodnia) and burnt down a rainbow installation in Plac Zbawicela, an artistic installation standing for diversity. After about two hours of marching and attacking the Russian embassy, the Polish police asked that the permit for the march be cancelled.*
I didn’t see anything in the blog post, or in the news article, which indicated that the art installation (which apparently is a traveling exhibit) was imposed by the EU.