That's wrong. Holding something in an IRA doesn't prevent you from selling it, only from taking the proceeds and putting them in your personal checking. The proceeds continue to be property of the IRA/401k, and can be re-invested elsewhere, without incurring a taxable event.
You can day-trade in your self-directed 401k or IRA until you're broke or Thiel-level rich, and the IRS will never get involved.
I mostly agree with the top-level comment, here; ProPublica is losing a lot of credibility for their mildly misleading and black-and-white framing of these tax issues, and I'm someone who genuinely believes that wealth inequality is a problem that can and should be addressed by the state.