Why is my wife receiving a biometric letter even though she is not applying for EB-5 with the I-829?

I applied for I-829 as the primary and only applicant. To completely and accurately disclose my information, I included my wife’s status on the form, but checked “No” on the question if she is applying with me. I paid application and biometric fees just for myself, and only received one I-829 receipt notice.

During my 2-year permanent residency, I successfully petitioned my wife’s I-130 and I-485. She is now a family-based, conditional permanent resident. But clearly, she is not part of the EB-5 program.

Today, I received 2 letters from the USCIS, saying both me and my wife’s fingerprints have been reused. To my surprise, on my wife’s letter, she is even assigned an I-829S receipt number, which I didn’t know before since I only received one I-829 receipt notice before.

I called the USCIS multiple times and the officers told me this is because of security reasons—as my spouse, she also needs to go through a background check. I also confirmed that the officers did not see any dependents or derivatives on my I-829 case.

Is this normal?