Spurious activation of Reverse ThrustIt looks like a spurious signal from the EEC drove the left Thrust Lever to idle to allow for an inadvertent deployment of Reverse Thrust (ala Lauda Air over Thailand). As Auto Thrust was engaged, the right engine will drive forward or remain in position to compensate for the loss of thrust from the left engine. It is this this assymetric condition that brought about the uncommanded bank resulting in the Auto Pilot tripping.
Thrust reverser is a mechanical mechanism, if the translation sleeve moves the warning light illuminates and crew action would be to shut the engine down. The auto throttle system will only command the climb power selected by LVL Change or VNAV, if the crew had selected VS mode in the last 1000 feet, the thrust adjusts according to the MCP speed.