Except in this article, where they assert that the funds were correctly reported to the government with no explanation of what that claim even means. And they’re not saying that the defendant claimed to have reported; Reason themselves are making the claim.

Like most publications, they have editorial constraints, and usually choose to discuss the breaking news rather than rehash older facts. Reason has been covering this highly complex and lengthy case for nearly a decade, they have published dozens of articles about it, unfortunately for you they did not address your specific question in detail in this particular article. I think if you dig a bit deeper you'll find answers.

edit - 2 minutes of searching past Reason articles:

That Lacey was convicted of "international concealment money laundering" is bizarre, since the money transfer was not concealed: His lawyer informed the IRS about it, as required by law. And it was not made for nefarious purposes, according to Scottsdale lawyer John Becker's trial testimony. Lacey had needed some place to park his savings after U.S. banks, scared by a years-long propaganda crusade against Backpage, had decided doing business with the company or its associates was a reputational risk. So Becker and another lawyer advised Lacey to deposit the money—$17 million, on which taxes had been paid—with a foreign bank.

It's hard to see how Lacey conducted a financial transaction "to conceal or disguise the nature, the location, the source, the ownership, or the control of the proceeds of specified unlawful activity," even if you accept the government's premise that this money was derived from unlawful activity. And, to be clear, I don't accept that premise, since Backpage's business should have been protected by the First Amendment (not to mention Section 230 of federal communications law).