It is very common for people to notice that ACT looks a bit like Gestalt or Emotional Focused Therapy. That links has been there from the beginning. Les Greenburg is on the back of the original ACT book for example. Why would that be?
Part of it is that contextual behavioral thinking helped establish Gestalt therapy.
Gestalt therapy never had much to do with Gestalt psychology -- even the Gestalt
psychologist that were still around rejected the comparison.
See the attached article for documentation and explanation.
Ralph wanted to call it integrative therapy ... think of how the history of psychotherapy might have been different had that happened. The ACBSers are just walking over that same ground.