Not a huge surprise, but it is always nice to see confirmation across the decades and from widely varying sources. Just as those BBC engineers decades ago tended to listen at substantially higher levels than the general public, if you go into a contemporary recording studio today, you will notice the much higher playback levels than most of us normally choose at home.This is not a huge surprise. The human auditory system has not changed in the last 100 years.
Though I guess it might have been possible that the higher quality audio we now have would result in a change in preferred listening level. Clearly though - not significantly.
Also it was interesting to see that musicians who were used to hearing live acoustic instruments chose to playback their music at levels that more closely mimic live music.