I found out about it from a link posted by someone in a thread about Spore (which had long since gone off-topic) on a forum (which isn't about Spore).
The person's first post about it, where he didn't mention it by name, was a rant about animal rights activists beginning with "It just happens that I read a news article to the effect that at one of the conventions for this simulator, there were many protesters outside. Guess who they were?" - He believed the fake news story posted on these forums.
Someone asked what simulator he was talking about, and he named it and linked to the "news article" (and the link went right to the fake news post on these forums). He later realized the article was fake and went "Oops!".
I stuck a link to the DarwinBots site in my Firefox bookmarks toobar, and about a week or so later, downloaded DB to try it out.