In English grammar, the scrupulously correct construction of the sentence you presented is as follows:
"Students receiving presurvey of their knowledge thought they did worse on this quiz
than did those who confronted the more comforting presurvey."
The phrase "than did those" is what's known as a comparative repeater phrase that more concisely and more succinctly replaces the longer phrase "than the participants" (alternatively "than the students"). Keep in mind that what is being compared here is the performance of the participants in the quiz ('worse...than"), not the participants themselves. (Notice that using the comparative repeater phrase provides substantial savings of several characters or letters of the alphabet.)
IMAGE CREDIT: CASTBOX.FM The version you suggested, ""Students receiving presurvey of their knowledge thought they did worse on this quiz
than participants who confronted the more comforting presurvey," missed out on the verb "did," which changes the sense of the original sentence altogether, thus wrongly comparing the participants themselves than their comparative performance in the quiz.
(I suggest though that you verify whether the statement you presented is faithful to the original statement in your source book. I seriously doubt the precision of its semantics. I would think that it would make much better sense if constructed this way: "Students receiving presurvey of their knowledge thought they did worse on this quiz than did those
who did not receive the more comforting presurvey." My point is that what's being compared here is the performance of students receiving the presurvey against those who didn't receive it rather than those "who confronted the presurvey," which is an altogether different--and I must say strange and tangential--comparative parameter.)
