Actual comments look like normal comment without upvotes.
What is this? An echo of migration from hashcode.ru?
Upon investigating this issue further it does seem that these are leftovers from the migration.
The most recent voting history we have in our databases (that I could find) is for April 2015 (Technically, March 31st, but oh well). This means that we do not have the actual votes for these comments and thus I can't say where they came from with certainty.
The migration theory is supported by the fact that the most recent comment with a negative score is from March 12th 2015, if it was from answers being turned into comments there would be more recent ones.