DISTINCTTech interview questions

The whole interview process was extremely unprofessional. Before I had an interview, HR had reached out to me asking a few questions regarding my start date, salary, experience etc.. I went in for an interview and it was perfectly fine, they were nice guys and seemed like a good company. A few days later I receive an email stating that they would like to offer me a position as soon as I tell them my start date. I had answered them a couple days after and did not recieve anything back. A week goes by and I send a follow up email regarding the offer and my start date. As soon as I send this email, I recieved an email from HR that I was not the right candidate for this position. HR reached out to me, not even the man I had the interview with. I automatically called him asking what had happened, wondering if this was a mistake and he then replied that he chose someone more qualified.. which is fine, but the fact he offered me a position before they were done the interviews blows my mind. He mentioned that HR was supposed to reach out to me a week ago when I said my start date but they forgot. Here I am not applying to jobs as I was offered something,and they take it away. Worst experience. Unprofessional.