Before the 2019 season, teams could still strike trades after the trade deadline if the players getting moved cleared waivers first. It was this system that allowed for the Tigers to trade Justin Verlander way back in 2017 despite it being the end of August when that deal went down. While the new system doesn't allow the Atlanta Braves to swing big league trades anymore, that doesn't mean that they can't still use the waiver wire to their advantage.
The Braves were roasted (and rightly so) for their inaction at the trade deadline.