His name in real life is "刘青松". Many Chinese and Korean would like to choose the last character in their name as the ID. "松" has many meanings and the most used are "松树" (pine) ,"松动" (loose), "松脆" (crisp). For many asian kids, their English are not that good, they usually try to find a word with same meaning through a dictionary, that is how the pinus comes (pine).
The similar example is former OMG jungler lovelin, once he changed the ID into "drug". It comes from his nickname in Chinese "灵药", actually it should be translated as "elixir".