So when I hear someone say they only read The Guardian, or reccomend it to people as a very reliable paper, my first thought is that they are in a bubble where they have no idea how biased and downright unreliable it is. Which I think is likely an accurate assessment.
My prejudice would be that they are right on people who want to feel good about themselves while maintaining their middle class comforts, and they are probably unknowingly to themselves paternalistic to minorities and even racist in some cases, and not deep thinkers.
But you know, I try to suspend my prejudices, and be aware that it would be actually allowing myself to get to know the person directly that would allow me to know and understand what they are really like, not making snap judgements based on my assumptions about their reading habits and trying to put them into little boxes. And I'd also try to keep in mind that many of us find we are in a bit of a rut until suddenly we have a new experience that makes us see how others see and experience things and that in no way precludes them being good people, just a bit naive perhaps.
If I did in fact get to know them, well, that would tell me more, and it would not be a surprise to find my instincts had been partly or even largely correct because after all, they are formed from experiences, but otherwise, as a rational adult with the capability to interrogate my own immediate impressions and judgements, that would be how I would leave my immediate impressions created by my mind about this person - with a sense of openness to who they are not defined by very small bits of information that might well play into my own limited experience.
And tbh I am really surprised that someone with this as an area of study would be so content as to just accept such prejudices without any real interrogation.