You're right that people tend to misuse the word "troll" for someone stating a differing opinion from theirs, in a way that they don't like (e.g. conservatives call liberals trolls, and vice versa). But at the same time, there has been at least one user making alt accounts in order to cause trouble, and make harassing comments on people's memes. I thought that was what most of the troll memes lately were referring to.
Also, sometimes users who have a number of popular memes refer to the people who put annoying comments on those memes (presumably motivated by jealousy) as "trolls." I don't know whether that's really the right use of the term or not.