"The first comprehensive look at the impact of all of Sanders' spending and tax proposals on the economy was done by Gerald Friedman, a University of Massachusetts Amherst economics professor. This more sweeping analysis was not commissioned by the candidate, though Sanders' policy director called it "outstanding work." Friedman has worked with Sanders in the past, but has never received any compensation." This is what you're referring to. How is this confirmation bias? He was never compensated by Sanders. Sanders asked him to crunch the numbers and he did. He may be a democratic socialist as well but numbers do not lie. He did not purposefully force the numbers to confirm his position.

Confirmation Bias also occurs when you alter the observations and predictions of a model to further a personal agenda, a gripe, your ego or ideology instead of interpreting correctly. This can either be done by omission, lying, misrepresentation or finding and supporting things that you believe in without logic in order to attract less educated individuals to your ideology. While it may not be biased, it sure as hell looks that way and if it walks like a duck, quacks like a duck...