I would assume that the use of 'appeared' is due to the apparent uncertainty of the evidence in comparison to the AAIB's own.
I disagree with 8pieced that all of aviation has let this crew down. Aviation is unfortunately built on evidence of errors, mistakes and misunderstanding. The Comet Mk1 being a prime example of new technology bringing new issues and unrecognised problems.
It is known that some components, on every aircraft you could name, occasionally fail and that, on return to the OEM repair station, there would be a test and nothing found. The item would be retested and reissued as serviceable "No Fault Found".
I put it to you that this was happening with Fuel sensors too...but no-one knew why because no evidence of water was present at the factory test...the water was probably displaced during the Tank Drain to remove the sensors.
I believe that no-one could have reasonably forseen this issue.