Well I agree, if you don’t talk you can’t lie. Plus many other reasons not to talk in general as FreedomPoster points out.
Thinking it over, I would guess it isn’t the text message itself they would be investigating but the potential crime of (in lay terms) intimidating a candidate for office. Just a guess.
Not only can you not lie, you cant be caught in a perjury trap. That’s how they got Scooter Libby and others. Just say that you have nothing to say.