Twitter's 5% was "Twitter users who logged in or were otherwise authenticated and accessed Twitter on any given day through Twitter.com or Twitter applications that are able to show ads".
Twitter's definition include lurkers while the 19+% number does not. And there are a lot of lurkers.
You likely refer to https://news.ycombinator.com/item?id=31397137 which looked at public active accounts over a 90 day period.
Twitter's 5% was "Twitter users who logged in or were otherwise authenticated and accessed Twitter on any given day through Twitter.com or Twitter applications that are able to show ads".
Twitter's definition include lurkers while the 19+% number does not. And there are a lot of lurkers.
As ramblerman pointed out at https://news.ycombinator.com/item?id=31397679 "25% of Twitter Users Produce 97% of All Tweets", citing https://www.pewresearch.org/internet/2021/11/15/2-comparing-... .