The ongoing refusal to answer questions under oath is.
He could have agreed to talk anytime and been released shortly.
It's a civil proceeding not a criminal proceeding so he would not be incriminating himself.
He could argue that by answering he would be admitting crimes and opening himself to criminal liability. But there's a possibly they give him immunity and that route is taken away.
I remember once reading two bits of news about people given similar sentences. One for copyright infringement, the other for sexual assault of a teenager.