Not necessarily. People "not being logical" might simply mean that their decisions are emotional. Emotions are not logical, but that does not make them random or wrong. There are still reasons for emotions, and frequently there's a large degree of truth to them as well. They often do exemplify bias, but that's why there's more than 1 person on the jury, and why attorneys are allowed to disqualify jurors, and why a good attorney will try to get a jury panel that is at least representative of the population if not favorably inclined to her client.