That happens a lot. There is a group of comment spammers that do one of the following.
- Nice Post or equal useless comment
- Flat out copy another users comment
- Copy chunks from various comments on the thread, and turn them into a new Frankenstein comment
#3 is harder but there are bots that do this for you, the idea is it is very on topic and can pass off as a real comment. No one wants to waste their voting power to flag, and they hope to get the random upvote. Since it is all automated, it costs nothing.
It's about the same value as ContentJunkie (and his alt's) posts.
Frankenstein comment...lol, yeah I 've seen a few of those also, usually pretty decipherable.