One mile is a believable data point for somebody who knows it's really tall and has no clue how tall buildings generally are and has no skills in estimating or reasoning to be able to come up with a good estimate, but I think "50 feet" as an estimate is not a legitimate data point. It is much more likely that somebody was being a smart ass, or wanted to screw up the experiment and make Hofstadter look silly, or had never heard of the Empire State Building (assuming Hofstadter didn't imply that it's a really tall building) and was just guessing for a random building (which it would still be a bad estimate for, but much less so).