Fact, according to Luke Jermay. Or at least it was true while he was working on the show.
Magicians have been known to lie every now & again.
Derren's usually honest about his dishonesty...
In that case, he can lie about anything, and not really be lying. He already told you he would be lying... just not about which part. Derren uses PLENTY of pre-show techniques. He just does then mid-show. Also, the definition of pre-show is different. Traditional pre-show happens before the entire show. With a television show, the pre-show could be the 30 seconds of talking, banter, or set-up that happens directly before the effect and gets subsequently edited out. As far as the finger throwing effect... there's a reason he doesn't do this in his live theater shows.