They had some equipment there that could identify drones via the radio signal, and trace it.
Here's a link to a story that tells of the equipment being used: https://www.krqe.com/news/balloon-fiesta/hundreds-violate-faa-s-no-drone-fly-zone-at-balloon-fiesta/1510662538
I was going into GSO earlier this year, at around 4000’ and 200+ kts, when one of these buzzed by us a couple of hundred yards away.
If it had hit the cockpit, I likely would not be here.