And testing confirmation bias in this fashion is intrinsically deceptive, so I probably have damaged my online reputation as well.
Yes, this test might not have passed a university ethics review - not only did you deceive your subject, which must be done carefully, but he didn't even know he was participating in an experiment!
It would have been passed by the IRB of Gwern U. As long as Gwern is not affiliated with another IRB, that's all that matters.
Master copy lives on gwern.net