The signal to close thrust levers in an autoland purely comes off one of the RAs. But I think Dimiair post 1013 is correct. If it's not to do with an autoland Retard, then the false RA indication is a false lead, a red herring. Alternatively, is there a possibility that with the A/T engaged, the sudden low reading of the critical 'faulty' RA produced a Retard demand? It doesn't seem very convincing.