From the artists Reddit thread:

Thank you! In Slavic tradition (it can be found in some Germanic and north Italian places too), the people would dress up as spirits to thwart the evil spirits, while also singing Christmas carols. This was originally a pagan tradition that got embedded in Christianity. They’d hold an avatar for the Sun, to signify that the Sun is returning, the days are getting longer. The tradition is generally called Koliada.

So, just people dressed up as spirits, looks sick though lmao