CBP is relentless in its mission to safeguard the nation’s borders and the privacy of all citizens. CBP’s biometric facial comparison technology is hosted within a secure cloud-based environment and does not store biographic data for any travelers. CBP retains U.S. citizen photos for no more than 12 hours after identity verification and only for continuity of operations purposes.

https://www.cbp.gov/travel/biometrics/privacy-policy

Is what they claim. What you saw may have been about non-citizens