If I apply rotation of 5 different angles and randomly cropp 10 different images from each rotated image and than divided into training testing and validation. Will it be totally incorrect evaluation of dataset?
Yes, it will be incorrect.
When you augment before splitting, it is possible that one crop of the test set appears in the training set, and the other in the test/validation set. This would leak information about the test set to the model during training, resulting in invalid evaluation.