Transfer learning is not used for resuming a task. When you use XGBTuner, the tuner maintains a cost model to predict the next schedule config to be explored. Usually the cost model is trained from scratch (random start, improved over trials). When enabling transfer learning with previous tuning log, the cost model will be trained by the tuning log instead of random start, so it is expected to predict a better next schedule config. On the other hand, the tuning process is still starting from the first trial.