when did IRC have hashtags for categorizing chatter? I've been on IRC for 10+ years, on dozens of networks, and I have no idea what you're talking about.
If you're referring to channel names, those aren't "hashtags". It was just a way to separate the difference between a channel and a nickname. IRC has also had "@","%", "+" and other symbols to identify operators and voiced nicks. None of which has any resemblance to @-replies, hashtags, etc.