What your father is doing is known as Straw Breathing, you inhale normally, then exhale via a drinking straw. Repeat for five minutes.

We're discussing bi-direction breathing training, wherein resistive inhaling is a significant part of the exercise regimen and one not offered in [easier] Straw Breathing.

If you have a study that compares Straw Breathing to using a Breathing Trainer it would be a welcome addition to the discussion. But currently straw breathing is primarily aimed at bringing people from below back to normal lung function, whereas breathing training is meant to improve lung function above normal.