Dear Ian, I don't know from where the information on Mr Thompson came, but I do know that, at the Public Record Office, they keep an archive of all the sailors in the Merchant fleet. I think the records start 1913, and quite a few of the surviving crewmen from the Titanic are to be found in this archive. I have seen the entries for some individual crewmen myself, so I have a feeling the information about Mr Thompson comes from this archive. Just a theory, however.
Best regards,
Peter