The NYT has a good summary at Judge Reverses His Order Disabling Web Site, but the headline is a bit misleading. In fact the judge didn't just vacate the TRO against Dynadot, as the full text of the order makes clear, he vacated both orders.
It's no so much a ruling on the merits as a recognition that there are substantial First Amendment issues, a real question as to whether the court has jurisdiction over Wikileaks if it is based outside the US, and that the order wasn't working anyway.
TROs and injunctions were part of the equity jurisdictions of courts (we've merged law and equity in the US, but the sources still matter sometimes). The court doesn't quote it, but there's an old maxim that “equity will not do a useless thing”. As much as anything, that, plus an excellent campaign of judicial education by EFF and the ACLU, explains the outcome.