Where did Oleg Tinkov go wrong when refusing from his American citizenship?

On March 5, the United States Department of Justice announced a list of charges against the head of Tinkoff Bank, Oleg Tinkov. Ministry officials insist that the banker deliberately hid some of his funds and didnэt indicate them in his tax return when he renounced his American citizenship. Three days earlier, there was the IPO of TCS Group, during which the value of Tinkov’s company share increased to $1 billion. But in the documents, the businessman announced only $300 thousand.
7 years later, the American Tax Service filed charges against the banker. In the Ministry of Justice documentation, it is indicated that he not only gave incorrect numbers, but also distorted information about taxable income. As a result, Tinkov was charged for providing false declarations and falsifying income data. He is now under house arrest in London, pending an extradition order, and has paid £20 million as bail.
American citizens who renounce citizenship are required to pay expatriation tax. It is calculated based on the amount that a citizen would receive if he sold all movable and immovable property at market value one day before renouncing citizenship. This is a one-time payment, which amounts 23.8% of the total sum.
Tax must be paid by persons whose fortune exceeds $2 million, as well as those whose total liabilities during the past 5 years amounted to at least $168 thousand. And also citizens who refuse a green card which was owned by them for more than eight years.
The government introduced these rules to combat money laundering, as well as to reduce cases of tax evasion.