No, in their minds, Christ was insufficient. They never fully trusted Christ's salvation. They just KNEW there had to be more to getting saved. And when the deceivers entered their midst and preached to them, they jumped at their demonic doctrines and denied Christ by trying to add works to faith. To them salvation became Christ AND ... something. Christ and celibacy. Christ and dietary laws. Christ and some act of denial. In other words, Christ and the efforts of the individual them self. They had never accepted that they could never make themselves acceptable to God. Thus they had never been saved. They may have given mental assent to Jesus in some fashion, but they had never recognized their hopelessness before God, their absolute inability to save themselves or to play any part in that salvation, and thus had never trusted in Christ alone for their salvation.
So, yes, they departed from the faith. But they departed because they had never had it in the first place. They superficially accepted it, but never believed it 100% in their heart. They professed it with their mouths so they could depart from it. Those who profess it in their hearts will never depart from it.