question shows 4 reopen votes have been cast.
review queue shows 3 wanted to reopen
Why is there the difference of 1 vote in between the two?
Not literally Who, but what type of user cast the 1 vote?
related although not my answer
The discrepancy is due to the fact that someone probably voted directly from the question and not the review queue. Only actions performed in the review queue will be recorded in the summary that you linked
This is not an inclusive list but one of the following are likely sources of the 4th vote: