I really can't understand how could a lawsuit like this were valid in the first place. The purpose of trademark is to prevent the counterfeit item be recognize

I really can't understand how could a lawsuit like this were valid in the first place. The purpose of trademark is to prevent the counterfeit item be recognized as the same as trademarked item. If the item is truly meant to refer the trademarked item, in this case realtime 3DCG rendering, there is no violation of the trademark. Isn't it? It's the same reason I can write any trademarked term here and not violate the trademark law. US law system is beyond my understanding.