Now that Ant-Man is officially in theaters, a number of interviews and articles have been posted that provide more insight into the film's post-credit scenes. In an interview with Entertainment Weekly, director Peyton Reed states that the second post-credit scene was added after seeing dailies from Captain America: Civil War. "When the dailies came in for the scene which is now the second tag, there was a moment that seemed to really complete the arc in our movie."
Reed added that originally some comedic tags had been envisioned for the second post-credit scene, featuring Michael Peña’s character in the film. Instead, it was determined that a second tag that ties to the Falcon's cameo and would set up Ant-Man's appearance in future MCU films would have a greater impact.
Another report indicates that the post-credit scene will actually appear in Civil War. "It's an actual scene from 'Civil War,' although it will probably play differently," according to Hitfix. "This is the first pass at the moment," which involves Bucky Barnes aka the Winter Soldier restrained in a basement with Steve Rogers and Sam Wilson talking about "how they're going to protect him." Steve and Sam reference "the accords" and Sam suggests they reach out to Ant-Man for assistance.
Hitfix also points out that the scene was directed by Civil War directors Joe and Anthony Russo and written by Civil War writers Christopher Markus and Stephen McFeely. Notably, it states that the scene with Sam and Scott Lang in the middle of Ant-Man was also scripted by Markus and McFeely.