Keras ModelCheckpoint Callback returning weights only even though both save_best_only & save_weights_only are set to False
Keras should be accessed as tf.keras now with tf2 ,so your import should be written as
tf.keras.callbacks.ModelCheckpoint

Keras own documentation as well as tf api documentation can be easily accessed for this purpose. Keras ModelCheckpoint class mentions the following arguments in official docs:
save_best_only: if save_best_only=True, it only saves when the model is considered the &quot;best&quot; and the latest best model according to the quantity monitored will not be overwritten. If filepath doesn't contain formatting options like {epoch} then filepath will be overwritten by each new better model.
save_weights_only: if True, then only the model's weights will be saved (model.save_weights(filepath)), else the full model is saved (model.save(filepath)).
So both 'save_best_only and save_weights_only'  have default value as False and will save all weights and full model if not True.