from the POV of people using irc from dialup it was indeed very much like that - but also from those who were dialing up to unix systems, or using them locally

from the POV of people using irc from dialup it was indeed very much like that - but also from those who were dialing up to unix systems, or using them locally over a network such as at a university, the machine running the irc client maintained a persistent network connection so it was possible to run a persistent client (or eggdrop bot) without disconnecting/reconnecting and re-entering channels. after about the year 2000 or so it was also really common to see people with shell accounts various places using gnu screen to maintain a persistent irc client session.