Muslims? was muhammad aware the first christians were catholic?

in the since they have images and they adopted the creed of Nicea, well a muslim told me on internet jehovah witnesses were closer to the real christianity becuase they don't believe in trinity and also I got answers here that christians today are not the same christians from the Quran because we have images and we believe in the trinity, I don't get if christians like catholics, orthodoxs and other old christian churches which live in the middle east aren't old? they were during the life of Muhammad, according to the islamic tradition if I am not wrong, he visited a nestorian monastery when he was a child and the monk told him he will be a man of God? well nestorians believe they are catholic but not roman