There are two versions of Ignatius's epistle to the Magnesians. But neither uses the word "Catholic". That term is found in his epistle to the church at Smyrna, where Polycarp was the bishop. Polycarp, who was martyred much later (around 155 AD), was also an 'auditor' [i.e. hearer] of the Apostle John. So was Ignatius, whose life long overlapped that of the Apostles. According to the fathers, Ignatius, the second bishop of Antioch (where believers were first called 'Christians') was ordained by Peter. Just read through all seven of his epistles (find them here), and the account of his martydom, and think about his proximity to the Apostles, and then ask yourself, who is more likely to be a better witness of the nature of the early Church: Ignatius or Luther?
Reading through the fathers is one of the things that coverted me to Catholicism after 37 years as a Protestant. The Church I found described in the fathers was the Catholic Church, not any form of Protestantism.
-A8