A little bit late but hopefully this can help someone else.

The `assortativity` function from `igraph` gives you the correlation between knn(k) and k, which is slightly negative in this case (-0.16) considering its values can range from 0 to 1.

The `knn` function gives you the knn only, not k. So when you plot `knnnet$knn`, you are plotting knn against an index assigned to each vertex. Your graph probably has around 80 vertices, that's why the x axis goes until 80.

To get the actual assortativity plot, try this:
`plot(degree(net), knnnet$knn, xlab = "k", ylab = "knn(k)")`. The plot should show more clearly the negative correlation.