You can find the opinion here (h/t Eugene Volokh).

I write about this case in Cheap Speech. I think, and the district court agrees, that it does not violate the First Amendment to make it a crime to lie about when, where, or how people vote. The Supreme Court so indicated in dicta in the Mansky case. That kind of “false election speech” can be limited consistent with the First Amendment even though laws regulating “false campaign speech” (such as statements that “my opponent voted six times to raise taxes”) likely cannot be.

(I am less sure about whether the existing statute that Mackey is prosecuted under covers this conduct).