Perfect score obviously means immune to political bias, heh. Yes you're right. This study does count as evidence (in the Bayesian sense naturally) that biases are relatively small though.

But there is an even bigger problem. People with eclectic politics might not identify with either mainstream left or mainstream right, disliking both their positions. Their may be fanatical and politically biased on something that dosen't map very well to the left-right scale, or they may be just so far left or right that regular positions basically don't seem that different.

In other words the study may be bad at measuring bias in political outliers. High IQ correlates with less moderate political opinions btw.