There is one turn around lane right before the border, but you have to be in the inside (fast) lane to access it. All of the other lanes have concrete barriers preventing you from changing lanes and getting to the last chance turn around. The San Ysidro border crossing is a very confusing place unless you have been there many times.
Seems to me that once he discovered that there was no turn around he could take, he could have turned off his vehicle and refused to go forward.