Perhaps the priest was rushing because he felt ill, and he sat down when he saw an opportunity to do so without disrupting the Mass.
I can think of several reasons for this. One of my prior pastors had leukemia. When his anemia was severe, or he was getting chemotherapy, he did have more trouble getting through the Mass. I also remember one dear priest who had to celebrate many years ago in our very small town, where there would have been otherwise no priest available until the next weekend, who had come down very suddenly with the flu (the flu is like that), who ‘rushed the Mass’, disappeared during the first readings (for obvious reasons), rushed the consecration, and sat for Communion. He just it made through the rest of Mass before having violent emesis and indeed had to go to the ER later that night for IV fluids.
There are some disabilities that don’t really ‘show’ that much. Myasthenia gravis or multiple sclerosis or Parkinson’s in the early stages for example–you can mostly have days where you function just fine, but then other days suddenly barely be able to walk. You can have COPD or asthma or emphysema that you manage most days with your inhalers just fine, but then be exposed to a potent irritant or allergen and barely be able to breathe.
I’d be inclined to give Father the benefit of the doubt here.