And was the waiver granted to the operator? I don't see on the application where you can request for a company to have a waiver (and any operator for the company can be covered).
I don't have any inside info on their airspace authorizations and waivers. But at that location, they were well below the Class B. I haven't checked the chart, but I suspect they were outside of PDK's Class D and that would put them in Class G. In that case, no airspace authorization needed (although there may have been a TFR in place).