There was a heist. The PCs did not perform the heist referenced. While the story does not lay out a single path for the PCs to conduct a heist, it is certainly possible for them to do.
To perform a hesit here, they'd need to figure out a way to a.) Locate the dragons, b.) Take the dragons, and c.) Not be caught taking them. That requires the PCs to plan and be inventive - not something they can lay down in a pre-stock adventure. They may have been able to have an NPC mastermind that created a plan and assigned the PCs roles to fill in the heist, but that would remove their agency and feel really streamrollered. I would not have been a fan.
Regardles - while it was not my favorite adventure, we did complete it and we did have fun.