IIRC in King v Burwell, the 4th circuit upheld the IRS interpretation, so the plaintiffs are asking the USSC to overturn the 4th Circuit, which affirmed the district court opinion against the plaintiffs. So, I think you are correct and I just had an incorrect impression of how the lower decisions went.
The Circuit Courts where split. In King v Burwell the 4th Circuit upheld the IRS interpretation, in Halbig v. Burwell the D.C. Circuit ruled in favor of the plaintiffs.