There's a link you can click to see the personal background of the respondents. It's tough to know what "researcher in a field not listed" means, but it's possible that over 60% are not even physicists:

    30.8% - A researcher in a field not listed above
    21.2% - A science enthusiast
    18.0% - A researcher studying quantum physics
    12.0% - A researcher studying astrophysics or cosmology
     9.2% - A researcher studying gravity
     8.8% - Other