If it wasn't there wouldn't be a 'retard and flare' capability (which is an auto land function only).
Retard is an speed mode only and has nothing to do with autopilot nor automatic landing (which is actually possible single channel, just not approved). You will see the FMA announce RETARD even on manual landings.
According to the Boeing bulleting posted above it was not a dual coupled approach but a normal single autopilot approach flown on Autopilot B.