Chat was always open even when moderators were not present. In the earliest days, registration was not even required. The difference, if I remember, was that registered (board access user) nics were in bold font. Those not in bold font were somewhat less trusted.
This would represent an obvious security flaw today. Anyone off the street had the ability to trade messages privately without being vetted whatsoever. Of course, the dumpster fire that is the internet of today was less deviant and more self-moderating back in those days (opinions may vary). And of course, it took several years for these clearnet sites to become easily located targets for vigilantes, trolls, and your general malcontents to require further measures to keep things legal, and with at least a slight modicum of civility.