Greta did an extensive segment on this yesterday. She actually drove the route he took, It’s very easy to make the mistake he did even in daytime.
The same thing happened to another Marine about 10 years ago. He volunteered to drive his truck, with his gun in it, from Camp Pendleton to the border to pick up some tipsy Marines. He missed the last exit and could not turn around before he crossed the border. Former Congressman Bilbray got him out of the Tijuana prison after about a month. That Marine got home, but his truck is still down there. I suspect the same will happen again.