First, it is not okay to show up in a tank top for the interview. I understand I am being interviewed, but YOU are currently the face of the company and YOU show the unprofessionality of it. Second, yawning while the candidate is answering the question is not very courteous to say the least (funny, I read here that another interviewed person experienced the same - the person who interviewed them was yawning through the interview. Just shows the overall professionalism level there and a question pops up "are they all that much NOT into their company and what they are doing there?") Third, if you ask me a question that partially involves technical background  - then know the technical part of it. Do not tell me I should've responded in a particular way when in fact I tried but you stopped me because you didn't understand what I wanted to say. Fourth, the first stage was to work on a case study, which was huge comparing to what other companies require, it involved lots of details that had to be researched about the company itself. If the person spent so much time and energy working on it, be respectful enough to get to know the candidate a little before having a video call with them (at least have their resume in front of you so you won't ask absolutely obvious questions - e.x., if you see I have a degree in STEM, do not ask me if I have a degree in STEM)