Thank you for your reply! I think I might understand now:
Since we set the feature extractor and box predictor to be detection_models feature extractor and box_predictor (detection_model._feature_extractor and box_predictor), the values for these weights in the detection_model get set to whatever values that are in the checkpoint for these specific weights?
And the other weights are still just random initial values since they are not provided as arguments to the checkpoint function, hence not restored?
Thanks!