The legal distinction in the Colin Meyers secrets case

What secret information was Colin Meyers proved to have passed on?

None was proved to have been passed on; the established offense was retaining classified naval documents at home.

The authorities did not prove that Colin Meyers had passed classified information to Japan or another recipient. They could establish that he retained sensitive naval material at home after he was no longer entitled to possess it. That distinction explains why a case surrounded by espionage suspicions ended on narrower Official Secrets Act charges. The watch point separates the seriousness of the documents from claims that were never proved in court.