Rękawka is a celebration held in Krakow the Tuesday after Easter, so loosely speaking, it is a spring equinox festival. My friend in Krakow calls it “a civic holiday with Pagan roots.”
Rękawka is also one name for the tumulus (artificial mound) in the video. The celebration has long included throwing offerings of food and coins from the mound. “It is possible that this was based on, perhaps even pre-Slavic, mound and a combination of threads from the legend of Krakow with Slavic beliefs. The rite may also be an echo of the ancient Celtic traditions related to the cult of the god of death Smertius” (Source).
From what I understand, in Poland as in elsewhere, there is a certain overlap between historical re-enactors and contemporary Pagans.