Among the men the council anathematised by name was Honorius I, bishop of Rome. He had written to Sergius of Constantinople in terms the council read as endorsing one will in Christ, and it condemned him with the others who had taught the doctrine. His successors confirmed the council and did not object to that clause.
For about twelve hundred years this was an awkward historical detail. In 1869 it became an argument. The First Vatican Council was debating whether to define papal infallibility, and the minority opposing the definition produced Honorius as the case that settled it: here was a pope who had taught error on a matter of faith, and an ecumenical council which had said so, and a line of popes who had agreed.
The reply given then, and still given, distinguishes between a pope speaking privately and a pope defining doctrine for the whole church. Honorius wrote a letter to one bishop, carelessly and in haste, without intending to settle anything; the infallibility defined in 1870 attaches only to a solemn definition made deliberately for the universal church, which this was not. The definition was drafted with that distinction built into it.
Whether that is a principled distinction or a boundary drawn around the evidence is a question people still answer according to what they already think about the doctrine. What is not in dispute is the record: an ecumenical council condemned a bishop of Rome by name, and the church has had to say something about it ever since.