Based on the article linked below, it seems that the money come from criminal activity:

> Wen tried to buy a string of expensive houses in London, but struggled to pass money-laundering checks and her claims she had earned millions legitimately mining Bitcoin were not believed.

> CPS chief crown prosecutor [..] said [...] cryptocurrencies "are increasingly being used by organised criminals to disguise and transfer assets [...]".

which is indeed money laundering, not tax evasion.