As I pointed out on the LW survey discussion thread, the anchoring question was much more closely related to the "what is your height in centimeters?" question than to the random number.

I've redone the comparison with all US responders who also gave a height (n=468). Not only is the correlation much stronger (r = -0.35 versus r = 0.08), but (in a sense) the effect is greater as well: while the random number slope is 0.15 here (+100 random number means +15 feet guessed), the height slope is -11.5 (+1 centimeter of height means -11.5 feet guessed).

I don't know what this says about bias. But interestingly, this effect is almost entirely killed by significant exposure to LW: among the (n=82) of the responders tested above who also had a karma score of at least 500, the correlation between height and estimate is -0.02, which is negligible. Among the (n=137) responders with a karma score of at least 100, the correlation is -0.064, and the slope of the effect is only -2.2 feet/centimeter.