Before they had even really come up with an overarching narrative for Captain America: Civil War, The Russos had a ton of concept art created to give them an idea of what they could visually do with the action in this movie.
Make sure to pick up Captain America: Civil War on Digital HD on September 2, and on Blu-Ray/DVD when it hits shelves on September 13.
They started off strong with Captain America: The Winter Soldier, they proved their overwhelming excellence with Civil War and we have a feeling that they will become legends when Avengers: Infinity War hits theaters in 2018.
What you were seeing there, I think once we started getting into the narrative, pretty early on, Ant Man was allied with Cap.