This may be facilitating misinformation by providing a quote that's not a quote and which is an exaggeration.
The quote from the indictment of the claimed false statement is that
"42 . . . a. SUSSMAN stated falsely - as he previously had stated to the FBI General Counsel - that
'he was not representing a particular client.' In truth and in fact, and as SUSSMAN had acknowledged to the Former Employee just days earlier, SUSSMAN was representing a client." (see indictment)(emphasis added)
https://www.documentcloud.org/documents/21080001-210916-sussmann-indictmentLegal commenters have stated that if this can be proved, it potentially could be convicted, and the materiality standard is so ridiculously overbroad that it shouldn't matter. I'm not trying to get into the weeds on this. If the statement were, as TheDrake hypothesizes, something like ~"I don't know who my clients' are," then I would agree this is another example of don't lie to the FBI about anything. But my attorney armchair observation of this is that it seems rational for this guy's defense to be ~"It wasn't a secret that my clients included the Clinton campaign, I had told people about that and the FBI knew. On that particular day I was not talking on behalf of any particular client, I genuinely thought this was something the FBI should check out." Unfortunately Sussman would need to testify and waive his fifth amendment to raise that defense fully, and go through a trial.
[If Sussman was indeed trying to pull a fast one, and saying, ~"aw shucks, I just came across this," because he was trying to obscure that he was indeed meeting with the FBI at least partly to further his clients' interest, then I'd say that was stupid. But even there this seems like a he said / she said as to his state of mind.]
With that, this seems more an example of "never talk to the FBI at all, because they can find a way to charge you for virtually any statement you make."
And also, wow, "don't try to play cutesy when you talk to the FBI."