Ticket Tailor UX/UI Designer | Developer interview questions

First interview was quite ok, with a charming Product Design person. After that I was assigned to do a small home task to design and develop in only HTML, Javascript and CSS (zero framework like React or Vue). I was invited to the technical interview, which supposed to be about the task but I had a 30min interview with 1 Fullstack (more Backend) and 1 Design person, mostly asking extremely Senior Level technical questions. Some of them were more related to the Backend than Front. What confused me the most, was the reason they don't use any frontend framework. When I asked about that, I was just bashed out like was some secret.