They would have said, OK, that is a theological term that does in an orthodox fashion describe Christ being of the same substance as God the Father, not a different one, etc.
Compare Augustine with the "orthodox" reading. Augustine again, first, just to rub it into your soul:
The body and blood of Christ consumed through faith without eating or drinking. Believe, saith Augustine, and thou hast eaten already.
“They said therefore unto Him, What shall we do, that we may work the works of God?” For He had said to them, “Labor not for the meat which perisheth, but for that which endureth unto eternal life.” “What shall we do?” they ask; by observing what, shall we be able to fulfill this precept? “Jesus answered and said unto them, This is the work of God, that ye believe on Him whom He has sent.” This is then to eat the meat, not that which perisheth, but that which endureth unto eternal life. To what purpose dost thou make ready teeth and stomach? Believe, and thou hast eaten already. (Augustine, Tractate 25)
Compare with Father John Bartunek, LC., whose interpretation requires the actual use of “teeth and stomach”:
“This was the perfect opportunity for Christ to say, “Wait a minute, what I really meant was that my body and blood will just be symbolized by bread and wine. Of course I didn’t mean that bread and wine really would become my body and blood. Don’t be foolish!” The strange thing is he doesn’t say that. He does not water down his claim, as if eating his flesh were just a metaphor for believing in his doctrine; on the contrary, he reiterates the importance of really eating his flesh and drinking his blood.”
Is the priest correct and in line with the orthodox understanding of Transubstantiation, or is Augustine?
Here is Augustine’s Tract 26 which goes throughout the rest of John Chapter 6. Chapters 15-20 provide more detail on Augustine’s Eucharistic Theology
http://www.clerus.org/bibliaclerusonline/en/index.htm
Augustine as I read him was talking to the Jews who were merely looking for food to eat that was of this world. So before he got to the notion of the Mana from heaven that God gave the ancient Jews thru Moses, he first had to challenge them that belief in him was essential and the first step before getting into the Eucharistic notions of the bread of life discourse. So on the Point where Saint Augustine is pointing out that Christ was trying to get the Jews to belief in him, once one believes, then the Eucharist becomes the next discussion and for believers, the Eucharist becomes the fullfillment of the mana in desert, so just as God gave the ancient Jews Mana to feed them in the desert on their journey from liberation from Egypt to the promise land, Christ sustains the believer with the sacrament of his body and blood during our journey from Baptism to our death when we will meet the Lord face to face.
Saint Augustine and Fr. Bartunek are making different theological points and while they are different they are not opposed to each other. I 1) Believe in the Holy Trinity [Faith in God] and 2) believe that God sustains me via the Eucharist.