Ask HN: Is it common practice for companies train interviewers on bad candidates

TLDR; I suspect I was used as a training dummy for HeadLandsTech staff, to get interviewers experience. Is this common place in the HFT/American industry? Or is this just me not wanting my ego hurt. Looking for honest answers as from an European perspective, this sounds crazy. Context: I've been programming since I was about 14, I've done well in my industry and I'm trying to change over to HFT. I've got a weak profile and I know it, I've sent out about 100 applications I've only gotten 2 answers so far. I tend to be brutally honest with myself and I am just here to get a reality check. The company I've been interviewing with is called HeadlandsTech and I made it through 4 rounds of technical test. In my estimation I aced 3 of them, 100% out of a 100% execution and did maybe 75% on the 3rd out of the four. After the 3rd one I felt like maybe I wouldn't get a follow up, but I did and I was very glad for it. The fourth interview was easy, and I implemented what was asked quickly, explained my reasoning and offered improvements or considerations in a real scenario. The interviewer seemed pleased and it was all around good. I got an email 1 day later that I would not be preceeding. This was quite a shock to me and I in the end I called their recruiting manager, who told me that I did not meet their technical bar. I restrained myself and told her quite politely that I had issues believing this, given that I really had aced the question given. It was a task I've done many times, and I've spent quite some time with various approaches and I discussed this with the interviewer. She told me the best she could do was to ask them for their feedback and that she would forward anything she got to me. I said ok and the call ended. 10-20 minutes later I got an email that they are unable to give an feedback at all to candidates. The fact that this person was so willing to lie to my face, and do something else when there was a written doesn't sit right with me and after looking it up more online, there was some hinting that certain companies use weak candidates as training for their interviewers. This fits with my experience, all the people who interviewed with me was very junior in the company and many of them asked very overlapping questions, seeming like there had been no coordination or red thread in the interview process. As I said, I am a weak candidate from my CV, but I tend to be honest with myself and my performances. I aced that last interview and I am feeling like I was given a test that I scored a 100% on, and now I'm learning that I was unpaid QA. I am really looking for honest feedback if this is actually a thing, or if I'm just doing wishful thinking to avoid having my ego hurt. Any feedback is welcome, thank you.