"In the statement he delivered on July 5, 2016, he described her email practices as “extremely careless.” He initially considered using “gross negligence,” but told Stephanopoulos that was a “lawyer term.”
“My staff convinced me that that's just gonna confuse all kinds of people, if you start talking about statutes and what the words mean,” he said. “What's a colloquial way to explain it? And elsewhere in my statement I had said ‘extremely careless.’ And so they said, ‘Just use that.’ And so that's what I went with.”
https://abcnews.go.com/Politics/comey-admits-mistakes-describing-clintons-sloppy-handling-classified/story?id=54487996