How to apply a Views filter to show fields if a radio button is not FALSE?
Often these kind of things come back to deciding how best to bend your requirements to suit the available logic. If I understand correctly, you have a radio button with the value of true, but no other options.

My immediate thought is to change it from a radio to a checkbox and set a default value as false (unchecked).

That way you just need to check for if true or if false and you don't need to concern yourself with if not false which does get tricky.