In fact, a simple test shows that the channels actually span outside the ISM/WiFi band.
What I did:
I configured my router to use a fixed channel, then started a heavy transfer (bandwidth test), and watched what happened on the DJI Pilot app's channel plot.
When I had set the router to channel 1 (WiFi channel), channels 11 to 15 in the DJI app went way up, with channel 13 maximized. No other of the 32 channels were affected.
Similar when setting the router to channel 7, the DJI channel 14 - 19 was affected.
And when setting the router to channel 13, the DJI channel 17 - 21 was affected.
So clearly, the hack seem to be real.
Assuming the DJI channels are equally spread, they will cover about 2,3 GHZ to 2,6 GHz.
With channel 1 selected on the router:
With channel 13 selected on the router: