Maybe this individual is saying, "I know I'm biased" as a sort of disclosure of where their views are coming from. If they did not say that they are biased, and it is later revealed that they are biased, then people would likely accuse said individual of misrepresenting his positions and claiming "objectivity" when he had no right to possess it. For example, had that person you quoted said, "IPhone was the best!" without me knowing that he had a bias in that belief, I might have sincerely believed him, and this could lead to terrible consequences, like me buying an IPhone instead of a potentially better version.

It's clear that this individual likely does sincerely and rationally believe whatever he believes, with or without his bias, but it's important to admit the existence of this bias to avoid accusations of "falsely portraying yourself as objective" later on. And it's better to disclose your bias rather than not mention it and end up having said bias be unmasked or revealed and you suffering embarrassment.