Positive and negative edges in a graph using Pytorch geometric

So I was looking about the definition of positive and negative edges in a graph. I came across this function train_test_split_edges in this page. According to this function the positive edges in a graph are the upper triangle in an adjacency matrix in a graph and the negative edges are the edges in the lower triangle of the adjacency matrix in a graph, assuming it is an undirected graph. This is my assumption , am I correct about my assumption.