“Level of interest” is listed as “not considered” in section C7 of http://opa.berkeley.edu/sites/default/files/uc_berkeley_cds_2014-15_april.pdf .
According to http://academic-senate.berkeley.edu/sites/default/files/committees/aepe/hout_report_0.pdf , spring admits are at the margin of admission, based on scores assigned by admission readers (at least two different readers, with a third reader added if the first two give very different scores). A high stat applicant admitted for spring may not have had the best essay and other subjective criteria, or gotten unlucky in getting two harder grading admission readers (they are supposed to be trained for consistency, but subjective things like essays still tend to vary in how they are judged).