If ONLY that guy could have been silent. He wouldn't shut up.ACLU suggests otherwise:
You have the right to remain silent or tell the agent that you’ll only answer questions in the presence of an attorney, no matter your citizenship or immigration status. You do not have to answer questions about your immigration status. You may simply say that you do not wish to answer those questions. If you choose to remain silent, the agent will likely ask you questions for longer, but your silence alone is not enough to support probable cause or reasonable suspicion to arrest, detain, or search you or your belongings.
It's so easy for us white folk to get across the border too.
BP: Are you a U.S. Citizen?
Me: Yes.
BP: Enjoy your day.