In one of the lectures in week 3 Andrew explained about anchor boxes. My impression is that it seems like the main reason for using anchor boxes is to enable the algorithm to detect more than one object in each grid cell. but in the programming assignment, the yolo_filter_boxes functions output values are not separated based on different anchor boxes and when applying the yolo_non_max_suppression function on them the boxes are in a way as if there is no difference between 5 anchor boxes. so for example, if there are both a pedestrian and a car in a specific grid cell finally one of them will be selected as a prediction. I will appreciate it if you correct me if I’m wrong.
sorry for the late answer. I am not sure if you still have the doubt or if you already solved it. Let us know. Might not be 100% following your question.