USCIS - Surprise inspection

About 3 Months back, my company had filed a petition to extend my H1B visa. The petition was approved about a month back.

Today morning 2 officials from USCIS paid a surprise visit to my office. They first spoke to the HR folks about details regarding my employment. I didn't know about this. Later my colleague came to my cube saying the immigration officials were here for a surprise inspection and asked me to bring my Drivers License/passport with me. So, I went to the conf room to meet the folks. My HR was present too. They asked me a few questions, which I have paraphrased here:
1. What is your title and what do you do here?
2. What is your salary?
3. How many hours do you work in a week. What are your hours of work/day?
4. Did your pay the H1B fees or did the organization pay for it?
5. What is your level of education? Where did you study? Where is the university? When did you graduate?
6. Is this only workplace or do I work from elsewhere too?

My answers were quite spontaneous, and I believe that's how they possibly get their cues from: i.e. spontaneity.

The officer then apologized for the surprise visit but said it was necessary so that I wasn't prepared or had any fabricated answers. They wanted to be sure that I was a valid H1b employee. He said that surprise checkups are done after the visa petition was approved.

Then I took leave and came back to my office. After a while, they again paid a surprise visit to my cube and took a photo of my cube with the name card in front of it. Proof, I guess. Funny, I thought.