I tried to reassure that this wouldn't be judged badly, but this had made me think why people have this opinion?
I think it's the traditional convention that an interview means showing up looking smart and "dressed to impress" however, interviews used to be reserved more for qualified positions and so understanding what constituted professional attire for the job was part of the interview. However, the culture in a lot of offices has relaxed over the years, so in the past if you worked in an office it was almost guaranteed you would be required to wear a suit (and probably expected to wear a skirt too) whereas now, a lot of offices are more likely to have a "smart casual" dress code.
Nowadays you get interviews for everything - from working on a building site to becoming a CEO - and so the people actually attending interviews are going to be assessed by different standard and therefore interview attire should no longer just be seen as strictly "office wear" but more "smart, relative to the industry".
If you're applying for a job on a building site, and turned up to interview in smart jeans, shirt, jumper and boots, you'd look smarter than you would in your work wear of work jeans, polo, hi-viz jacket and work boots you would be seen as looking smart.. However, if you turned up to an interview for a management position in the city in that outfit, when work wear would be suit and tie you would look like you hadn't made an effort and didn't understand the expectations. Also, if you showed up in a suit and tie to an interview for a job in a more casual company, I'd wonder if you actually comprehended the job or the working conditions as it would look like you had totally misunderstood the industry standards.
Then, in between those two extremes, a lot of offices (especially ones where there isn't a lot of customer interaction) have a much more relaxed culture overall, including work wear. So while you can't turn up in a tracksuit, a suit would be too much and smart jeans are more than acceptable ... yet a lot of people, including PPs on this thread, still have the mindset that "interview = always wear a suit" rather than "interview = something smart for that industry/office/company".
I used to teach in Spain and the schools I have worked in have always had a very relaxed view of workwear as a teacher - as long as it was sensible, practical and presentable (ie clean/in good condition) then it was fine. I used to work with one primary teacher in his early 20s that I only ever saw wear jeans, polo shirt, hoodie and trainers as did most of the Sixth Form students. If a stranger walked in they would have struggled to tell which of the jeans/hoodie/trainer wearing people was the teacher if they saw them all in the corridor, but he was one of the best teachers in the school and I learned a lot from working with him, regardless of what he wore.