As someone who did a lot of hiring in my last job, I would push back against the narrative here that it's about lying or behavior policing. Although there is plenty of truth that there's an unfair bias against negativity, I do think there's a very valid reason for hiring managers to care about whether or not an applicant can remain positive or at least objectively neutral in an interview, and be diplomatic about negative experiences.

Invariably, at any company, even if they are a fantastic workplace, you are going to disagree with your lead or coworkers at some point. You will be asked to do work you aren't excited about or don't see value in, and you will be asked to work with people you don't particularly like.

If you aren't able to maintain a fairly positive attitude for a one hour interview, it makes sense that a hiring manager might worry about how well you'll be able to be a team player when things get rough. I used to think it was bullshit, and I learned the hard way. I hired someone who was fairly unpleasant during his interview, because he was the most competent applicant, and it seemed wrong to me to look at anything other than job skills. He was an excellent programmer, but he sucked so much time and energy out from the rest of the team with complaints and arguments. Of course I don't think that's always going to be the case, sometimes people have gone through genuinely negative past work experiences or just have brusque personalities, but I was certainly wary after that of people who couldn't put on a positive attitude for an interview.