So, there's a few things to unpack here. Exit polls, that is what happens when people think unweighted raw data is the correct data. When doing exit polls, some people are more likely to answer than others. Older people are the least likely, people of color are less likely, young people are the most likely, so demographically, the raw data would oversample Bernie's demographic. After they get the raw data, they have to compare it to the actual voting demographics and adjust to fit the the voting population, not the answering population. 

As to the studies by Berkeley and Stanford math department. There's no such thing. There is a report by a couple of students, not professors, not researchers, not the college. The authors did not present it as a study by the college, but Bernie supporters misrepresented their "report" as something official which is pretty reprehensible since it damages their reputation and will lead people to think they lie. It is also bad statistical analysis,