bug fix: switched rows and cols for correct detections in confusion matrix (#2883)

utils/metrics.py

@@ -145,7 +145,7 @@ class ConfusionMatrix:
         for i, gc in enumerate(gt_classes):
             j = m0 == i
             if n and sum(j) == 1:
-                self.matrix[gc, detection_classes[m1[j]]] += 1  # correct
+                self.matrix[detection_classes[m1[j]], gc] += 1  # correct
             else:
                 self.matrix[self.nc, gc] += 1  # background FP