As others have pointed out, the guy may be pretending to have misinterpreted the way the program works in order to reduce his penalty. Other than his statement, there's no indication that Amazon does pay drivers to return packages never assigned to them. He may also have genuinely misinterpreted the rule and been unlucky enough to get caught his first time trying to game the system.

Even if their system has the flaw described by the theif, their package tracking system would be pretty poorly designed if it can't be trivially modified to prevent drivers from returning packages not assigned to them.

I imagine they also datamine non-delivery and missing package rates by neighborooh, day-of-week, driver, and a few other factors and flag suspicious drivers. This probably means having a given driver cover a patchwork of different neighborhoods on on irregular schedule to reduce the effect of a driver being unlucky enough to get assigned a high theft neighborhood on a high theft day of the week.

If they find the package return rates are really too high, it's easy enough to just pay all drivers to return to the warehouse at the end of their shift. However, that probably costs significantly more and is inconvenient for drivers.