There are two obvious reasons why this statute does not apply to Comey's situation.
First, note the word "concealment." This is a stand-alone element of the offense, not just a superfluous verbal flourish restating the point that one must report. Just look at any federal pattern jury instruction: affirmative steps to conceal are required, not just the fact of failing to report the crime. See, e.g., Lancey v. United States, 356 F.2d 407, 4010 (9th Cir. 1966) (silence alone, without affirmative act of concealment, is insufficient). There is no basis for claiming that Jim Comey took affirmative steps to conceal any alleged obstruction by Donald Trump. To argue that Comey somehow affirmatively concealed something by taking care with who got to see his memo entirely collapses this distinction, and would extend liability for misprision to just about every criminal investigator and prosecutor in this country (given how routine it is for both investigators and prosecutors to create but limit circulation of documents with evidentiary content in this sense).
Second, and more fundamentally, Jarrett's op-ed implies that the obligation to report runs specifically to Justice Department prosecutors. That's not what the statute says, however, and of course the more obvious recipients for any such notificiations would be...the FBI. Jim Comey was, of course, FBI Director at all relevant times, and deeply engaged in supervision of existing, related criminal (and probably also counterintelligence) investigations. It's more than a stretch to suggest that the misprision statute somehow creates a "two-person" requirement for knowledge of possible federal crimes, such that it is not enough for one FBI person to be aware of the possible criminal behavior. A "crooked cop" scenario would of course be different, but no one is alleging (nor could they) that Jim Comey was in cahoots with a plan to obstruct the Flynn investigation.
Third, even if misprision concerns required Jim Comey to convey knowledge of Trump's actions to others at FBI, it remains quite possible that he did exactly this.