It's an old saw: people hear what they want to hear and see what they want to see.I don't think it worked that way. I think it was an idea developed while reviewing and synthesizing other research studies.
Which is to say, yes, the thesis itself could be born of confirmation bias. Maybe they found what they wanted to find.
I must be honest, though: I found a lot of value in my old Social Psychology textbook, even though most everything in it were lessons I had already learned from behind the stick. (I'm a street philosopher.

Anyway, this looks intriguing. Thanks for posting, mgarbowski!