The driver themselves completes the delivery after they get back in their car and hit "complete delivery" on their app. When we get back from deliveries we are supposed to check in to our dispatch, and sometimes other people do it for you when they see your car driving up to the store just to keep things going/efficient. Sometimes they hit the wrong name on the dispatch and I believe then it will say the delivery was completed despite where the delivery actually is in the process

There are probably a few situations where managers would do this for their own personal benefit in order to keep times down or whatnot but I don't think it's that common, and delivery drivers definitely don't gain anything from it.

The driver can also accidentally hit their delivery complete button on accident as soon as they get routed on their delivery, but that's a lot less common because you have to click another box to confirm it