While I gather Jerome is the only person who explicitly equates "the gospel of the Hebrews" with Matthew, I think this connection is fairly obvious in the remarks of other church writers. Take Origen, for example. In EH 6.25.4 he is cited as saying:
Among the four Gospels, which are the only indisputable ones in the Church of God under heaven, I have learned by tradition that the first was written by Matthew, who was once a publican, but afterwards an apostle of Jesus Christ, and it was prepared for the converts from Judaism, and published in the Hebrew language.
Here we see that he thinks the NT Matthew was originally written for Jews in Hebrew and that it was translated into Greek.
And in his Commentary on John 2.6 he cites a verse from "the gospel according to the Hebrews" and defends it with a (or in my view,
another) verse in Matthew (even though a similar version is found in Mark):
If any one should lend credence to the gospel according to the Hebrews, where the Saviour Himself says, My mother, the Holy Spirit took me just now by one of my hairs and carried me off to the great mount Tabor, he will have to face the difficulty of explaining how the Holy Spirit can be the mother of Christ when it was itself brought into existence through the Word. But neither the passage nor this difficulty is hard to explain. For if he who does the will of the Father in heaven [Mt. 12:50] is Christ's brother and sister and mother, and if the name of brother of Christ may be applied, not only to the race of men, but to beings of diviner rank than they, then there is nothing absurd in the Holy Spirit's being His mother, every one being His mother who does the will of the Father in heaven.
I don't think there was a "gospel of the Hebrews" apart from the Hebrew Matthew and its translations. In other words, there was a gospel that was written for Jewish Christians in Hebrew which they called Matthew and which orthodox Christians thus described as being "the gospel according to the Hebrews" and from which they believed the NT Matthew was translated.
But I think orthodox Christians were not entirely correct about the NT Matthew being a translation of the Hebrew Matthew, since I think it only incorporated parts of one or more translations of it (in addition to Mark). And I suspect its incorporation of parts of the Hebrew Matthew is what led to the NT Matthew being called Matthew. Even though it also incorporated Mark, it couldn't be
called Mark because
Mark was already known and called Mark (as per Papias). So it became known as Matthew because of its connection to the Hebrew Matthew.
And I think this is why citations of "the gospel of the Hebrews" differ from the NT Matthew, because the latter only consists of
parts of the former. The NT Matthew doesn't have the part about Jesus calling the holy spirit his mother that Origen cites or the resurrection appearance to James that Jerome cites because those things didn't survive the author of the NT Matthew's editorial process. But "the gospel of the Hebrews" (i.e., the gospel that Jewish Christians used and which they called Matthew) was still NT Matthew-like enough for orthodox Christians to associate it with the NT Matthew.
This might sound confusing, but I think the situation is simple.
1. Mark (in Greek) and Matthew (in Hebrew) were written first (in whichever order) and multiple translations were made of the latter.
2. Parts of one or more translations of the latter were incorporated into the NT Matthew in addition to Mark (thus making it the first gospel "harmony").
3. The NT Matthew wasn't called Mark because Mark already existed, so it was called Matthew because it contained (via translation) parts of the Hebrew Matthew.
4. Because Papias said that Matthew was originally written in Hebrew and translated multiple times, orthodox Christians believed that the NT Matthew was translated entirely from the Hebrew Matthew, and they explained away the differences between the latter and the former as being due to Jewish Christian mutilation and forgery, which I think is true for the Ebionite Matthew, at least, but not for the Hebrew Matthew that was used by Nazarenes. In other words, I think the Ebionite Matthew
and the NT Matthew had "mutilated and forged" the original Hebrew Matthew.