Unfortunately, the web site did not explain that.
Good catch. I was suspecting as much, and I believe anyone who thinks about it for a moment would recognize that allowing the office holder to issue a rebuttal statement would seem like a reasonable requirement. How anyone could construe this as "negating" the effect of the petition is beyond me. If I were just a bit more cynical, I'd suspect a disinformation campaign by the foes of the petition.