Look at that last sentence again: “The Greek text, however, is in substantial conformity with the original.” The author of that Introduction in the Confraternity Bible is stating that as if it were a known fact. It isn’t. Very little is known about the “Hebrew” (or Aramaic) Matthew. That assertion about “substantial conformity” is, quite simply, unverifiable.
St. Matthew is the subject of Chapter 3 of St. Jerome’s De Viris Illustribus (“Illustrious Men”). Along with a few brief remarks by Papias, Irinaeus, Eusebius, and Origen, this passage in Jerome is one of the prime sources among the Church Fathers for all that is known about the “Hebrew Matthew”. What follows is the whole of Chapter 3:
• Matthew, also called Levi, apostle and aforetimes publican, composed a gospel of Christ at first published in Judea in Hebrew for the sake of those of the circumcision who believed, but this was afterwards translated into Greek, though by what author is uncertain. The Hebrew itself has been preserved until the present day in the library at Caesarea which Pamphilus so diligently gathered. I have also had the opportunity of having the volume described to me by the Nazarenes of Beroea, a city of Syria, who use it. In this it is to be noted that wherever the Evangelist, whether on his own account or in the person of our Lord the Saviour quotes the testimony of the Old Testament, he does not follow the authority of the translators of the Septuagint but the Hebrew. Wherefore these two forms exist: Out of Egypt have I called my son, and for he shall be called a Nazarene.
That is pretty much everything that is known about the “Hebrew Matthew.”