Well, what we know is that the Gospel of Barnabas is not part of the Bible, and never has been.
So, whatever is in it, it has NO bearing on Christian theology, although a LOT of New Testament “scholars” may make much of it.
Its just Apocrypha. There are lots of them that surface from time to time—Like the Gospel of Judas, or the Gospel of Pontius Pilot. What IS the verses that seem to imply a coming of Mohammed? It might refer to many other things or saints.