Well, I can't tell you why anyone chose to vote one way or another, and I haven't voted on this thread at all. But you ask a fair question, so I hope giving you my guess will help.
Your answer, though clear, is not helpful. If you're going to give someone an "RTFM" answer, at least give them an URL they can follow, like perlfunc:grep or grep. The questioner may not know how to use perldoc at all. It looks like the questioner went to some effort to ask his/her question reasonably clearly, provide a code sample, and so on, but your response is just a throwaway. It looks demeaning; I don't know if that was your intention, but it comes off that way.
Read 1st monasterians to remember the spirit of how to answer questions. If you can't/don't want to put some effort into a good answer, that's OK. Someone else will step in. But a put-down answer doesn't help anyone, you or the questioner.