where's Garaganta then?. suddenly Kubo is going to change it all of a sudden?. he already came through Garganta and broke through the illusion (or at least that's how it would look to anyone under the actual hypnosis), hence is why it looks like he's breaking through a glass mirror and not appearing through a black hole.
also, when someone does "come through garganta" the garganta itself is made aware first, before the actual person appears through. hello!.