Zscaler Software Engineering New Grad interview questions

Video call interview walked through my resume, all projects and Intern experience. Onsite interview was worst with one of the interviewer. Easy questions on using hash maps and data structure related questions. Some basic c++ questions and OS related questions. I had not mentioned c in my resume and they expected socket programming, this they informed me only during the onsite round. This was the reason they gave me for my rejection as well. My question to the HR and video interviewer guy is, if they wanted a specific skill why dont they tell me at the beginning. HR certainly bragged a lot about the company , stock values and they handled me so badly through their interview process. I am very lucky i got rejected from them. Organization is definitely doing very good. The HR who handled my candidacy and 1 interviewer onsite are probably the worst people i have come across interviews. I certainly look at reviews on glassdor and i have never written reviews till now. This company interview process made me do so.