The section of the Catechism speaking on those who do not now know the Catholic Church “through no fault of their own” are a category of folks, theoretically unknown to Christianity, who have, by an outward showing of grace, do come to Christ though never united with the official Christian church.
With regards to Protestants, yes of course they’re all saved, granted they accept the fundamentals of Christianity: repentance unto life, total need of God’s Grace, and accepting Christ as their Savior.
The Catechism says that all other Christians are “separated brethren” which are united with Catholics in an “imperfect communion.” So…when the Catechism says that there is no salvation outside the Catholic Church, remember it is saying that all Christians are technically in communion with the Catholic Church, hence, fall under this. This is why when Protestants become Roman Catholics, they are not re-baptized…because they are already members of Christ’s catholic (catholic means universal) Church.
Be careful how you define Christians though, since the Church does not recognize Mormons or Jehovah’s Witnesses, for example, as Christians.