A tree is a type of graph. Is the headline meant to reveal the fact that not all graphs are trees (which is obvious) or is it meant like "not all graphs are tre

A tree is a type of graph. Is the headline meant to reveal the fact that not all graphs are trees (which is obvious) or is it meant like "not all graphs are trees, and here's how you deal with those non-tree graphs?" Even then I'm confused about the title of the article.