To me it seems like both components in the following graph are trees since they don't contain any loops. Therefore the graph should contain a forest. But according to the quiz that I'm trying to solve that is wrong. Is it because an isloated node does not count as a tree? Why would that be the case?
Isolated vertex is a tree and indeed, a graph with only one vertex is called trivial tree. Since there is another disconnected tree in the graph, this should be a forest I think, there must be a mistake in the quiz.