A very excellent point about the radio. We had tons of trouble setting up a net of temperature monitors in our server room for this very reason. Anything with an antenna is a possible way for data to leak - and even things without antennas if you have the right equipment and know what to look for.
The tempest world is wildly fascinating. Anyone with interest should look up what Léon Theremin said long ago about classified conversations in rooms with fluorescent lights. Or just look up tempest examples. Theremin himself designed a number of very successful bugs and listening devices. Computers and connected devices also have a long history of having emanations being listened to to extract information. Even electric typewriters and the current pulses they put on the local wiring and RF they gave off. (https://en.wikipedia.org/wiki/Tempest_(codename))
It’s amazing all the ways important information can be teased out of devices and systems, and even the operators. People monitoring morse code communications back in WWII could identify the “fist” who was transmitting and with triangulation could watch troop movements. It was as if the soldiers had tracking devices which in effect they did.
I’m guessing FlightAware won’t be seeing data from the Pro Plus, though.