The switch is what is being tested yes, but it is not clear that what is being measured in the switch is “AI fried their brains” rather than “context switching in the middle of a test”. If they wanted to make that point it would be useful to have the maths test run with a calculator group who also got it yanked halfway through, that way we would be able to see what proportion of the effect is over dependence on AI removing critical thinking and what amount is having your methods disrupted mid task.