The student is under stress due to their struggle with the passage, which the author isn't taking creative liberties to describe as that's how most people will react.
The time constraint wouldn't be an issue if they were comfortable with the passage. You can give them unlimited time and they might provide a sufficient response, or just quit and move along in the study, which also stated in the reading.
And, with all due respect, I think you're probably giving yourself more credit for your ability to perform better than these students than what might be the actual result, but that's not atypical for me online community, whose denizens are a cut above the rest...
This was also noted in the study:
* [...] However, these same subjects (defined in the study as problematic readers) also believed they would have no problem reading the rest of the 900-page novel.
Keep in mind that the students were English majors, so understanding complex classical works might be expected at some point.