Thew real reason they ask questions, as this fool already knows, is to hear you speak. CBP agents are trained to listen for the very subtle differences between native-spoken English and English that which was aquuired after age 2. No one who learns any language after learning another fluently is completely free of the accents, inflections, words patterns, etc. of their first language.
Back in the day, there were certain phrases they would lead Eastern Eurpeans to speak, and in doing so, they could detect a Russian native pseaker as opposed to a German, Yugoslav or other person who could get into the US more easily.
In addition, since they make no record of the persons answers to these questions, this idiot is simply a ballbreaker.
/johnny
>>Thew real reason they ask questions, as this fool already knows, is to hear you speak.
Actually this fool (above) is out of date by a few decades.
They know very well he is American. The real reason they ask is to look for signs of stress, no accents.