Answer:
Much of this depends on his immigration status when he committed the crime. If we assume he had illegal status and If he was ordered to leave, he would not be allowed reentry for 5-20 years, if ever. Even if he had a green card, he would be barred from reentry. He was most likely barred from reentry because of a felony. A felony charge will ensure no reentry. The officer was correct.
These are for trafficking, each state will have other laws.
The U.S. Code, Title 22, Chapter 78 – Trafficking Victims Protection
The Victims of Trafficking and Violence Prevention Act (TVPA)
The Customs and Facilitations and Trade Enforcement Reauthorization Act of 2009
The Intelligence Reform and Terrorism Prevention Act of 2004
The PROTECT Act of 2003
The Civil Asset Forfeiture Reform Act of 2000 (CAFRA)
The Mann Act of 1910