You asked what "Open Borders" meant. I'm telling you that to most, it means a flat-out unrestricted access into a country. I'm not sure why you're trying to angle that requiring a Passport is akin to unrestricted entry. It isn't. You know as well as I do that you wouldn't be allowed into Ireland had you not presented that valid Passport. So, no, requiring a passport to enter the U.S. would not be how most people would view the idea of open borders. They would view it as requiring nothing at all - zero documentation.
To your other question, which I think you were ultimately trying to lead someone into a debate over, I'm not aware of anyone directly advocating for this among the democrat candidates. I think many are interpreting the positions of a few of them of decriminalizing unauthorized entry as a somewhat de facto open borders position.