I might be going out on a limb here but...is it possible that Lightoller's vague and ambiguous statements were also due to mental exhaustion and maybe a little PTSD? The American inquiry started the day after
Carpathia arrived in New York and these people were immediately swept up and subjected to all these questions. These poor guys had no time to really gather and process what they had been through. In Lightoller's case, the guy was standing on an overturned lifeboat in the North Atlantic less than a week ago, was very likely wanting to go back home, and probably was in no mood to be buried under an avalanche of inquiry questions.