No they weren't "all slaves". Manumission was a fairly common practice in Deep South states, and in the Southern ports, there did exist a rather prosperous free black class, and many of them would go on to form volunteer units for the Confederate Army, granted the lions share of these units originate from Louisiana.
According to the 1850 census, there were black slave owners in every state that became the Confederacy.
Nonsense. Manumission was actually difficult in most southern states. An 1838 decision by the Alabama Supreme Court, Trotter v Blocker (6 Porter 269), ruled that manumission was a gift and that legally slaves were ineligible for receiving such a gift. A North Carolina case, State v Newsom, ruled that blacks had no legal rights under the Constitution. And an 1822 law in Mississippi required approval of the state legislature to manumit a slave. Every southern state had laws preventing free blacks from moving into the state, and some like Virginia had clauses in their constitutions requiring slaves freed to leave the state within 12 months or be sold back into slavery. Those who were freed in all southern states were restricted as to what work they could do, where they could live, and who they could marry.
...and many of them would go on to form volunteer units for the Confederate Army, granted the lions share of these units originate from Louisiana.
Such units did not exist.