I'm curious about that myself, and how it would affect the civil suit. When you consider that he refers to "girls" in both his book and video, how damaging is it to mention an accusation of grooming/abusing a 14-year-old? I think he could make a case that such an accusation is damaging, but it would not be easy to determine liability. Again, this depends on how Crotian law/courts deal with such matters, but in the US you can win a defamation case but have the damages reduced if you are considered to be at least partly liable.
That also raises another question- is the civil suit just for show? There is no reason for any of the plaintiffs to make the trip out there to defend themselves. Otherwise, the case could have been extremely embarrassing (and even more damaging to his reputation). Imagine calling him to the stand for a cross-examination? Imagine calling family members, or others who know him and have worked for him, to testify? He almost certainly will not have to go through that, so he can continue to brag and bluster on Twitter without the fear that he'd be exposed.