I'd say that while a single comment on a forum might not be enough to identify you, the sum of your comments can easily do (because of pieces of personal information you let slip in this or that comment); then everything you write must be considered personal data, unless there is a way to tell apart or remove the personal information from your comments.
Think about pictures: the picture of a landscape you took on a holiday doesn't identify you, but other pictures in your library might do (they contain faces, places, etc.). All together, the pictures can tell who you are and where you've been and when and with whom.
Think about pictures: the picture of a landscape you took on a holiday doesn't identify you, but other pictures in your library might do (they contain faces, places, etc.). All together, the pictures can tell who you are and where you've been and when and with whom.