If they think the procedure is to read the next question when the previous one has been completed, and they do, even if the other person is screaming, they think they're "following rules". They're not the ones who came up with the procedure.
Which is the whole point: the participants were trying to follow rules, even if they made mistakes in following those rules. The idea that there was a total "breakdown" of the rules doesn't seem supported at all.
Your point is fair, but what is really nuanced is that the people who 'stopped' were the best ones at following the rules.
This seems interesting to me - they were conscientious about 'what was happening' - not just blithly following orders.
The 'rule followers' maybe were conscientiously applying the 'spirit of the test' and quit when they realized it was not reasonable.
The others were 'pressing buttons'.
Even then, it's subject to interpretation. There's a perfectly rational reason why people might subject to 'following the rules' if that's what they've been asked to do and have a sense of 'dutiful civic conduct' and 'trust in institutions'.
Instead, most participants rushed through, most likely to end their own negative experience. Which is much more nuanced that "gosh, they told me to do it."