If this was a scientific experiment, then what you consider 'very reasonable explanation' I would call a lot of hand-waiving to explain away the difference betw

If this was a scientific experiment, then what you consider 'very reasonable explanation' I would call a lot of hand-waiving to explain away the difference between the theory and the experimental outcome. He gets away with it because he doesn't need to convince his fellow scientists, only a bunch of pupils. But it is nevertheless quite unscientific.