This is because of Reddit's Vote Fuzzing. The upvotes and downvotes shown are not the actual amount of votes. From the Reddit FAQ:
How is a submission's score determined?
A submission's score is simply the number of upvotes minus the number
of downvotes. If five users like the submission and three users don't
it will have a score of 2. Please note that the vote numbers are not
"real" numbers, they have been "fuzzed" to prevent spam bots etc. So
taking the above example, if five users upvoted the submission, and
three users downvote it, the upvote/downvote numbers may say 23
upvotes and 21 downvotes, or 12 upvotes, and 10 downvotes. The points
score is correct, but the vote totals are "fuzzed".
How is a comment's score determined?
According to the same principles as a submission's score.
A comment's score is simply the number of upvotes minus the number of
downvotes. If five users like the comment and three users don't it
will have a score of 2. Please note that the vote numbers are not
"real" numbers, they have been "fuzzed" to prevent spam bots etc. So
taking the above example, if five users upvoted the comment, and three
users downvote it, the upvote/downvote numbers may say 23 upvotes and
21 downvotes, or 12 upvotes, and 10 downvotes. The points score is
correct, but the vote totals are "fuzzed".