You are absolutely right on this point. I misread the sentence. I stand corrected.
I will say that I don't think it helps the case much for his infallibility, though, to say that he was a Satanically inspired, passive dupe - "a fit tool for his will", as they put it.
As far as passivity as a Satanic tool goes, he was not completely passive. The Council proclaimed: "But but along with them, it is our universal decision that there shall also be shut out from the Church and anathematized the former Pope Honorius of Old Rome, because we found in his letter to Sergius, that in everything he followed his view and confirmed his impious doctrine."
Cordially,
Infallibility applies only to ex cathedra definitions.
he followed his view and confirmed his impious doctrine."
According to Vatican I, the pope speaking ex cathedra involves "defin[ing] a doctrine regarding faith or morals to be held by the universal Church." Honorius may have passively confirmed heresy, but in the same letter he sought to impose silence about the issue. That is not defining a doctrine to be held by the universal Church.
After the letter fell into mischievous hands, Honorius was apparently adopted as the poster child for a new heretical movement. If this happened against Honorius' will or after his death, he is not fully to blame. Authorities seeking to crush the heresy 50 years later, condemned its poster child in the strongest language they could muster. The anger of the counsel was probably directed more at the current heretics than at Honorius personally. It is hard to defend oneself in a "trial" held 50 years after death. If the old pope had still been living, perhaps he would have pleaded ignorance and shown some repentance. The council verdict may well have been overly harsh on Honorius. His letter said its contents were meant to be kept in silence and therefore not to be held by the universal Church.