Please dig into that book. There are clear errors and gaps in understanding above.

Evidence of original sin is rich in both the OT and NT, humans with imperfect dominion over their faculties, a will that vacillates, an intellect that cannot see the truth because the senses have clouded its view of moral matters, a body that complains moving the will against the good.

Then there are particular references - all well before "Augustine" to the condition.

When David says in Psalms: "Behold, I was brought forth in iniquity, and in sin my mother conceived me." he was referring to what the Church eventually termed Original Sin.

When Saint Paul....again well before Saint Augustine says in Ephesians that all people who are not in Christ are “sons of disobedience”  he was referring to the condition of Original Sin. The name came later.

I could go on but I implore you to stop "teaching" and pick up that book, setting aside the pride of a little knowledge, and go get a lot more