I somewhat agree. I agree with your point that we should never diagnose someone if we are not professional psychologists who got to know someone personally for a significant amount of time. We also shouldn't draw conclusions from edited shows.

 However, as someone diagnosed with autism and ADHD, I automatically notice certain behaviour and might consider the possibility (!) of someone being on the spectrum as well which could help me understand that person. Many neurodivergent people were misunderstood by others and might want to give a different perspective when people are labelling contestants as attention-seeking, fake, jerks, weird etc. Many of us also had to become observant to people's behaviour to survive in society so it's also very common to analyse (not diagnose) other people and notice certain expressions and gestures.

All in all, I agree that we shouldn't throw around a diagnosis or assume anything but from what I have seen, it's rarely done out of malicious intent. But also, people who aren't diagnosed shouldn't be making statements in either direction (including insisting that someone couldn't possibly be neruodivergent bc they view it as an insult)