The gemorah has stories of amoraim not judging cases after receiving even the most minute favor. What were the amoraim suspect of?
The basic pshat is that shochad blinds(for details, see Toras Moshe [the bible] and its Meforshim).
You can be a good person as still make a mistake. So that rabbis didn’t judge cases where there was even the most minute amount of potential bias. It would seem that to use someone with a huge bias (every son looks up toward his father and presumably he was chasidic himself) to bring proofs like this is weak. he is not suspect for anything. Its just not the strongest proof.