I was stopped and extensively questioned upon entering the U.S. from Canada via land border. I am an American citizen who was taking a roadtrip to Canada with my own car from California. Why did it happen?

The queue of cars at the port of entry was rather short and most of the other cars were Canadian.

The primary officer referred me for secondary inspection without giving me any reason. The secondary was empty so I walked straight to the CBP greeting them with warm "Hello". They needed to express their superiority by yelling at me that "we haven't called you yet!". Bossy indeed!

Then I was asked bunch of question about my trip to Canada. They took my car keys and went to search my car while I was waiting inside the room. It took them good 20-30 minutes. No idea what took them so long. (A conspiracy theory, could they plant a devide in my car? )

After they returned they stamped my passport and the exit card form and I was on my way out. I asked but they gave me no reason for the extensive search, only "We just wanted to enjoy your company".

Funny thing is there was nobody else but me at the time. Why did they pick me? Why did they choose to harass their own citizen?

Will this happen again when I cross the border? Am I flagged in a computer somewhere?

I was not expecting they'd lay out a red carpet for me but a nice words like "Hello and welcome home" would make my day better. This experience left a bitter taste.

Is this typical? Anyone with similar experience? Sorry I know this forum has to do mostly with flying, but I figured it might be somewhat relevant still.