In what context did you see it?
Some aircraft use magnetic sensors for the controller sticks and that's what it usually refers to, and airplane mode doesn't change a thing, it's about the magnets that are there to hold it in the charger.
If your phone and watch is connected with wifi or i think Bluetooth the 2.4ghz make interference if you use a 2.4ghz from skycontroller and anafi. Try 5.8ghz i think is free of interference.