In a lot of the European leagues, the top scorer on each team is demarcated by something on the uniform. In the NLA (top Swiss league), their jersey literally says “TOP SCORER” surrounded by flames. In the Liiga, the top scorer gets a shiny golden helmet. I’m guessing that that game was very early in the Liiga season, so Pulli was the top scorer and therefor got to wear the special boy helmet.
I remember watching Sasha Barkov wear that helmet all year long in 2012-2013. What a special prospect he was.