I also got the HSB on my CBP receipt while returning to the US in Chicago ORD.

I have Global Entry, but got an X on my receipt (it might've been because the unclear photo at a bad angle taken by the machine), which required that I visit a CBP booth (still through the expedited Global Entry lane, yay). The CBP officer thought I appeared really sick (I had a minor cold), and wanted to get the CDC check me out, but they had left for the day. He then requested his supervisor, who asked me if I had been through Kenya. The supervisor told the officer that I looked normal for someone with a cold and to just let me through. As the officer handed me my passport and receipt, he urged me to see a doctor ASAP, to which I replied OK with a furtive eye-roll. He noticed my insolence and immediately pulled the receipt out my hands, angrily scribbled out whatever he initially wrote, replacing it with HSB, asked me about the duration of my trip and my occupation, typed something into his computer, and then dismissed me with a blank look of self satisfaction. At the exit podium, another CBP officer saw the HSB notice on the receipt and sent me to secondary screening, where two other officers took my passport, looked something up on the computer, questioned me, and went through my luggage, which all took about 15 minutes. I'm glad it was relatively quick and that the secondary officers were at least friendly.