Its tricky what happens with -t: if you ask for the top-100 terms, it requests the top-100 terms (by docFreq), then resorts the top-N by totalTermFreq.
So its not really the top 100 most frequently occurring terms.
Using the -t option can be confusing and slow: the reported docFreq includes deletions, but totalTermFreq does not (it actually walks postings lists if there is even one deletion).
I think this is a relic from 3.x days when lucene did not support this statistic. I think we should just always output both TermsEnum.docFreq() and TermsEnum.totalTermFreq(), and -t just determines the comparator of the PQ.