This is I-8, the last CP is in East San Diego county. They are manned by the BP and have assistance from the CHP. Primary use is in alien smuggling and narcotic interdiction including the money involved. About 5-10 miles N of the border, in an area rife with smuggling of both kinds. Likely had a dog sniffing his car while he was waiting. The Ag CP he refers to is on the Az/Cal border, also on I-8. They ask if you have any fruits or other agriculture products with you.
At the 2:57 minute mark, the driver says "Where else can I go through sir but highway 35" when he's questioning the TSA, and goes on later stating it's 25 miles from the border. So I-8 is also highway 35?