No, that isn’t what happens. If you have been selected for interview then you are a strong candidate for that role. The interview is your opportunity to sell yourself. You would be amazed how many people dont!
“Everything” is never equal! Most interviewers will be looking for people who present themselves in a professional manner. Accepting that candidates will be often be nervous, you are looking for people who display commensense and leadership. You want people who display those core “notech” skills that will be essential to the next stage of the process, that being training. Central to those skills are communication, but there are many others, and the interviewers will be looking for some evidence of those in somebody who otherwise appears well rounded, knowledgable and pleasant.
An interview will never be an infallible process or a perfect filter, but it is a well trodden path and much of what is expected shouldn’t really come as a surprise to candidates. This is a technical role in a customer focussed industry. An interviewer can reasonably expect the candidate to be well groomed and professionally and smartly dressed. They should have a good broad knowledge of the company. They should have a good broad technical knowledge. They should communicate well. The interviewers (who are all individuals working as a team) are looking for people who must also be able to do the same. From the interview they are likely to select those individuals who are likely to fit in the companies corporate culture, and whose technical background suggests a very high likelihood of success at the next stage.
Nobody is selected as decoration or garnish. Everybody has the opportunity to be selected further. Despite that, it is surprising how many people fail to research or prepare adequately. A good interviewer will be well aware that a candidate may be stressed or nervous and they should be able to put the candidate at some degree of ease in order to bring the best out of them, after all it is “the best” that you want to hear. They would also expect a candidate for this role to be able to deal with a certain degree of stress. Candidates presenting themselves with some form of “distraction” (casual dress or grooming, dirty shoes, etc.) does rather suggest either a lack of research, understanding, or commitment to the role, and will have done nothing to enhance their chances.