The Precision-Recall plot on page 17 caught my eye (Extended Data Fig. 3a). Specifically the grey area. "...grey shading indicates the valid range between perf

The Precision-Recall plot on page 17 caught my eye (Extended Data Fig. 3a). Specifically the grey area. "...grey shading indicates the valid range between perfect performance and a random classifier." What's with the diagonal cutoff at the bottom of the plot? I understand where the dotted line comes from, but I expected the grey shading lower bound to stop at the dotted line entirely.