That's not the right use of literally, and at best, is a good use of hyperbole. 20 years is a long time. 20 years ago, SMS wasn't a thing, and IRC and internet chatrooms were more popular. As time goes on, you have things like MSN, Yahoo! Messenger, etc. Emoji were invented after 20 years ago.
Lookit, I love Slack. Used it extensively in a huge team.
But I do get tired of the constant thing around HN whenever a company releases some new feature, people immediately post a "Well, credit should really go to XYZ who did it first".
Sometimes the other company did launch a similar feature first, sometimes the features aren't that similar, and more often than not, everyone is copying from everyone. (and that's ok)