I was responding to the OP’s question directly:
Why did this one student get accepted to all of their reach schools?
This one student was accepted to all of their reach schools because all of the offices that reviewed this student’s application had the same reaction to it for whatever holistic reasons. Thus, they were accepted to all of the reach schools. What appealed to the offices is probably not predictable as it is highly subjective and might change based on unpredictable institutional priorities and/or the current application season environment.
Only collision could result in a more equitable admissions outcome for comparable, equally qualified students in the same school or social orbit.
That’s all I have to say on this topic.