The OUT logic, all doors closed and parking brake released, pre-existed phone apps by many years. When phone apps came along, the started to display information about the flight's status and the recording of an OUT time was the best available proxy for when the airplane has departed the gate and started to taxi. There is no intention to, nor benefit from, deceiving.

By policy, we can not release the parking brake until all doors are closed, the purser has reported that the cabin is prepared for pushback, our Before Push checklist is complete, and the ground crew is ready to capture the nose-wheel and push us back. (Many of our tugs can not capture the nosewheel until the brakes are released. You may notice this process when the airplane is slowly pulled forward a few feet between the door's closing and the beginning of pushback)

When there is a delay between brake release and pushback it is most commonly due to ramp congestion behind us. When brakes are released, we call the applicable ramp controller to request pushback and are often told to Hold. Sometimes that hold can be lengthy but we rarely have any idea how long it will be.

In this case, it sounds like after preparing to push, the crew learned that they were going to wait at the gate until closer to their wheels-up time. At that point, the brake was likely set again, but that doesn't trigger an IN time, which would be a return-to-gate (RTG), until an aircraft door is opened. The IN time was later generated when passenger door was opened and that showed the RTG in the app.

As a passenger, we are app-centered but the internal IT structure of airline operations is not. The app was an add-on to a system that had been evolving over many decades as technology advanced. The apps try to present the information, which is formatted for use by the airline employees in doing our jobs, in a way that is understandable and informative to the passengers. Sometimes details get lost in the translation.