Blizzard originally trademarked Heroes of the Storm on September 24, 2013 in the United States and September 25, 2013 in Europe. Mike Pohjola applied for a Finnish trademark for his table-top game on October 4, 2013. This is all public knowledge available by searching the US and EU trademark databases. At the time of Pohjola's application, we didn't know what Heroes of the Storm was exactly. On the surface, Pohjola's application seems to be in response to that original leak. Myrskyn Sankarit may have existed earlier, but the name was never registered with any trademark office until after Blizzard registered their own. Any potential issues in Finland, where the game has already been published, is a question for someone who knows more about trademark law.